Skip to content

Euler's Formula

Mechanics of Materials · FE Reference Handbook section

Mechanics of Materials
11 formulas
10 exam-style examples
~60 min
All Mechanics of Materials lectures

Handbook notes for this section

Definitions and conditions exactly as the handbook states them.

  • Theoretical effective-length factors for columns include:
  • Critical buckling stress for long columns:

Core formulas for this FE topic

Definitions, applicability, units, assumptions and worked examples for each relation.

Worked exam-style examples

The four ways this section is written on the real exam — thoughts first, then equations, then substitution.

Example 1
Euler buckling load — solve for critical load — Euler's Formula

A mechanics of materials problem uses Euler buckling load. Given modulus (E) = 10,000 ksi; moment of inertia (I) = 110.0 in⁴; effective length factor (K) = 1.5000; unbraced length (L) = 98.0000 in, determine the critical load (Pcr) in kip.

Given

  • modulus(E)=10,000ksimodulus (E) = 10,000 ksi
  • momentofinertia(I)=110.0in4moment of inertia (I) = 110.0 in^{4}
  • effectivelengthfactor(K)=1.5000effective length factor (K) = 1.5000
  • unbracedlength(L)=98.0000inunbraced length (L) = 98.0000 in

Find

critical load (Pcr), in kip

Start with the thinking

  • The governing relation printed in this handbook section is Euler buckling load.
  • Everything except Pcr is given, so isolate Pcr symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2
  2. Step 2 — Rearrange the relation so that Pcr stands alone on the left-hand side.

  3. Step 3 — List the givens: modulus (E) = 10,000 ksi, moment of inertia (I) = 110.0 in⁴, effective length factor (K) = 1.5000, unbraced length (L) = 98.0000 in.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    Pcr=502.4 kipPcr = 502.4\ \text{kip}
  6. Step 6 — Check: returning Pcr = 502.4 kip to

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2

    reproduces the given quantities, and both sides carry the same units.

Answer:
Pcr=502.4 kipPcr = 502.4\ \text{kip}

Why the other options are there

  • 1,005 — kept a factor of two that cancels in the correct rearrangement.
  • 251.2 — dropped that same factor in the other direction.
  • 552.7 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Euler's Formula

Example 2
Euler buckling load — solve for modulus — Euler's Formula (2)

A mechanics of materials problem uses Euler buckling load. Given moment of inertia (I) = 130.0 in⁴; effective length factor (K) = 1.4000; unbraced length (L) = 196.0 in; critical load (Pcr) = 4,262 kip, determine the modulus (E) in ksi.

Given

  • momentofinertia(I)=130.0in4moment of inertia (I) = 130.0 in^{4}
  • effectivelengthfactor(K)=1.4000effective length factor (K) = 1.4000
  • unbracedlength(L)=196.0inunbraced length (L) = 196.0 in
  • criticalload(Pcr)=4,262kipcritical load (Pcr) = 4,262 kip

Find

modulus (E), in ksi

Start with the thinking

  • The governing relation printed in this handbook section is Euler buckling load.
  • Everything except E is given, so isolate E symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2
  2. Step 2 — Rearrange the relation so that E stands alone on the left-hand side.

  3. Step 3 — List the givens: moment of inertia (I) = 130.0 in⁴, effective length factor (K) = 1.4000, unbraced length (L) = 196.0 in, critical load (Pcr) = 4,262 kip.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    E=250114 ksiE = 250114\ \text{ksi}
  6. Step 6 — Check: returning E = 250,114 ksi to

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2

    reproduces the given quantities, and both sides carry the same units.

Answer:
E=250114 ksiE = 250114\ \text{ksi}

Why the other options are there

  • 500,229 — kept a factor of two that cancels in the correct rearrangement.
  • 125,057 — dropped that same factor in the other direction.
  • 275,126 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Euler's Formula

Example 3
Euler buckling load — solve for moment of inertia — Euler's Formula (3)

A mechanics of materials problem uses Euler buckling load. Given modulus (E) = 12,000 ksi; effective length factor (K) = 1.0000; unbraced length (L) = 102.0 in; critical load (Pcr) = 4,724 kip, determine the moment of inertia (I) in in⁴.

Given

  • modulus(E)=12,000ksimodulus (E) = 12,000 ksi
  • effectivelengthfactor(K)=1.0000effective length factor (K) = 1.0000
  • unbracedlength(L)=102.0inunbraced length (L) = 102.0 in
  • criticalload(Pcr)=4,724kipcritical load (Pcr) = 4,724 kip

Find

moment of inertia (I), in in⁴

Start with the thinking

  • The governing relation printed in this handbook section is Euler buckling load.
  • Everything except I is given, so isolate I symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2
  2. Step 2 — Rearrange the relation so that I stands alone on the left-hand side.

  3. Step 3 — List the givens: modulus (E) = 12,000 ksi, effective length factor (K) = 1.0000, unbraced length (L) = 102.0 in, critical load (Pcr) = 4,724 kip.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    I=415.0 in⁴I = 415.0\ \text{in⁴}
  6. Step 6 — Check: returning I = 415.0 in⁴ to

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2

    reproduces the given quantities, and both sides carry the same units.

Answer:
I=415.0 in⁴I = 415.0\ \text{in⁴}

Why the other options are there

  • 830.0 — kept a factor of two that cancels in the correct rearrangement.
  • 207.5 — dropped that same factor in the other direction.
  • 456.5 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Euler's Formula

Example 4
Euler buckling load — solve for critical load (case 2) — Euler's Formula (4)

A mechanics of materials problem uses Euler buckling load. Given modulus (E) = 12,000 ksi; moment of inertia (I) = 45.0000 in⁴; effective length factor (K) = 1.0000; unbraced length (L) = 90.0000 in, determine the critical load (Pcr) in kip.

Given

  • modulus(E)=12,000ksimodulus (E) = 12,000 ksi
  • momentofinertia(I)=45.0000in4moment of inertia (I) = 45.0000 in^{4}
  • effectivelengthfactor(K)=1.0000effective length factor (K) = 1.0000
  • unbracedlength(L)=90.0000inunbraced length (L) = 90.0000 in

Find

critical load (Pcr), in kip

Start with the thinking

  • The governing relation printed in this handbook section is Euler buckling load.
  • Everything except Pcr is given, so isolate Pcr symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2
  2. Step 2 — Rearrange the relation so that Pcr stands alone on the left-hand side.

  3. Step 3 — List the givens: modulus (E) = 12,000 ksi, moment of inertia (I) = 45.0000 in⁴, effective length factor (K) = 1.0000, unbraced length (L) = 90.0000 in.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    Pcr=658.0 kipPcr = 658.0\ \text{kip}
  6. Step 6 — Check: returning Pcr = 658.0 kip to

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2

    reproduces the given quantities, and both sides carry the same units.

Answer:
Pcr=658.0 kipPcr = 658.0\ \text{kip}

Why the other options are there

  • 1,316 — kept a factor of two that cancels in the correct rearrangement.
  • 329.0 — dropped that same factor in the other direction.
  • 723.8 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Euler's Formula

Example 5
Euler buckling load — solve for modulus (case 2) — Euler's Formula (5)

A mechanics of materials problem uses Euler buckling load. Given moment of inertia (I) = 265.0 in⁴; effective length factor (K) = 1.0000; unbraced length (L) = 208.0 in; critical load (Pcr) = 2,753 kip, determine the modulus (E) in ksi.

Given

  • momentofinertia(I)=265.0in4moment of inertia (I) = 265.0 in^{4}
  • effectivelengthfactor(K)=1.0000effective length factor (K) = 1.0000
  • unbracedlength(L)=208.0inunbraced length (L) = 208.0 in
  • criticalload(Pcr)=2,753kipcritical load (Pcr) = 2,753 kip

Find

modulus (E), in ksi

Start with the thinking

  • The governing relation printed in this handbook section is Euler buckling load.
  • Everything except E is given, so isolate E symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2
  2. Step 2 — Rearrange the relation so that E stands alone on the left-hand side.

  3. Step 3 — List the givens: moment of inertia (I) = 265.0 in⁴, effective length factor (K) = 1.0000, unbraced length (L) = 208.0 in, critical load (Pcr) = 2,753 kip.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    E=45539 ksiE = 45539\ \text{ksi}
  6. Step 6 — Check: returning E = 45,539 ksi to

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2

    reproduces the given quantities, and both sides carry the same units.

Answer:
E=45539 ksiE = 45539\ \text{ksi}

Why the other options are there

  • 91,079 — kept a factor of two that cancels in the correct rearrangement.
  • 22,770 — dropped that same factor in the other direction.
  • 50,093 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Euler's Formula

Example 6
Euler buckling load — solve for moment of inertia (case 2) — Euler's Formula (6)

A mechanics of materials problem uses Euler buckling load. Given modulus (E) = 20,000 ksi; effective length factor (K) = 0.7000; unbraced length (L) = 74.0000 in; critical load (Pcr) = 1,801 kip, determine the moment of inertia (I) in in⁴.

Given

  • modulus(E)=20,000ksimodulus (E) = 20,000 ksi
  • effectivelengthfactor(K)=0.7000effective length factor (K) = 0.7000
  • unbracedlength(L)=74.0000inunbraced length (L) = 74.0000 in
  • criticalload(Pcr)=1,801kipcritical load (Pcr) = 1,801 kip

Find

moment of inertia (I), in in⁴

Start with the thinking

  • The governing relation printed in this handbook section is Euler buckling load.
  • Everything except I is given, so isolate I symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2
  2. Step 2 — Rearrange the relation so that I stands alone on the left-hand side.

  3. Step 3 — List the givens: modulus (E) = 20,000 ksi, effective length factor (K) = 0.7000, unbraced length (L) = 74.0000 in, critical load (Pcr) = 1,801 kip.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    I=24.4818 in⁴I = 24.4818\ \text{in⁴}
  6. Step 6 — Check: returning I = 24.4818 in⁴ to

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2

    reproduces the given quantities, and both sides carry the same units.

Answer:
I=24.4818 in⁴I = 24.4818\ \text{in⁴}

Why the other options are there

  • 48.9636 — kept a factor of two that cancels in the correct rearrangement.
  • 12.2409 — dropped that same factor in the other direction.
  • 26.9300 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Euler's Formula

Example 7
Euler buckling load — solve for critical load (case 3) — Euler's Formula (7)

A mechanics of materials problem uses Euler buckling load. Given modulus (E) = 14,000 ksi; moment of inertia (I) = 300.0 in⁴; effective length factor (K) = 1.5000; unbraced length (L) = 177.0 in, determine the critical load (Pcr) in kip.

Given

  • modulus(E)=14,000ksimodulus (E) = 14,000 ksi
  • momentofinertia(I)=300.0in4moment of inertia (I) = 300.0 in^{4}
  • effectivelengthfactor(K)=1.5000effective length factor (K) = 1.5000
  • unbracedlength(L)=177.0inunbraced length (L) = 177.0 in

Find

critical load (Pcr), in kip

Start with the thinking

  • The governing relation printed in this handbook section is Euler buckling load.
  • Everything except Pcr is given, so isolate Pcr symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2
  2. Step 2 — Rearrange the relation so that Pcr stands alone on the left-hand side.

  3. Step 3 — List the givens: modulus (E) = 14,000 ksi, moment of inertia (I) = 300.0 in⁴, effective length factor (K) = 1.5000, unbraced length (L) = 177.0 in.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    Pcr=588.1 kipPcr = 588.1\ \text{kip}
  6. Step 6 — Check: returning Pcr = 588.1 kip to

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2

    reproduces the given quantities, and both sides carry the same units.

Answer:
Pcr=588.1 kipPcr = 588.1\ \text{kip}

Why the other options are there

  • 1,176 — kept a factor of two that cancels in the correct rearrangement.
  • 294.0 — dropped that same factor in the other direction.
  • 646.9 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Euler's Formula

Example 8
Euler buckling load — solve for modulus (case 3) — Euler's Formula (8)

A mechanics of materials problem uses Euler buckling load. Given moment of inertia (I) = 150.0 in⁴; effective length factor (K) = 2.0000; unbraced length (L) = 95.0000 in; critical load (Pcr) = 2,226 kip, determine the modulus (E) in ksi.

Given

  • momentofinertia(I)=150.0in4moment of inertia (I) = 150.0 in^{4}
  • effectivelengthfactor(K)=2.0000effective length factor (K) = 2.0000
  • unbracedlength(L)=95.0000inunbraced length (L) = 95.0000 in
  • criticalload(Pcr)=2,226kipcritical load (Pcr) = 2,226 kip

Find

modulus (E), in ksi

Start with the thinking

  • The governing relation printed in this handbook section is Euler buckling load.
  • Everything except E is given, so isolate E symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2
  2. Step 2 — Rearrange the relation so that E stands alone on the left-hand side.

  3. Step 3 — List the givens: moment of inertia (I) = 150.0 in⁴, effective length factor (K) = 2.0000, unbraced length (L) = 95.0000 in, critical load (Pcr) = 2,226 kip.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    E=54280 ksiE = 54280\ \text{ksi}
  6. Step 6 — Check: returning E = 54,280 ksi to

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2

    reproduces the given quantities, and both sides carry the same units.

Answer:
E=54280 ksiE = 54280\ \text{ksi}

Why the other options are there

  • 108,560 — kept a factor of two that cancels in the correct rearrangement.
  • 27,140 — dropped that same factor in the other direction.
  • 59,708 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Euler's Formula

Example 9
Euler buckling load — solve for moment of inertia (case 3) — Euler's Formula (9)

A mechanics of materials problem uses Euler buckling load. Given modulus (E) = 10,000 ksi; effective length factor (K) = 0.7000; unbraced length (L) = 79.0000 in; critical load (Pcr) = 3,554 kip, determine the moment of inertia (I) in in⁴.

Given

  • modulus(E)=10,000ksimodulus (E) = 10,000 ksi
  • effectivelengthfactor(K)=0.7000effective length factor (K) = 0.7000
  • unbracedlength(L)=79.0000inunbraced length (L) = 79.0000 in
  • criticalload(Pcr)=3,554kipcritical load (Pcr) = 3,554 kip

Find

moment of inertia (I), in in⁴

Start with the thinking

  • The governing relation printed in this handbook section is Euler buckling load.
  • Everything except I is given, so isolate I symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2
  2. Step 2 — Rearrange the relation so that I stands alone on the left-hand side.

  3. Step 3 — List the givens: modulus (E) = 10,000 ksi, effective length factor (K) = 0.7000, unbraced length (L) = 79.0000 in, critical load (Pcr) = 3,554 kip.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    I=110.1 in⁴I = 110.1\ \text{in⁴}
  6. Step 6 — Check: returning I = 110.1 in⁴ to

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2

    reproduces the given quantities, and both sides carry the same units.

Answer:
I=110.1 in⁴I = 110.1\ \text{in⁴}

Why the other options are there

  • 220.2 — kept a factor of two that cancels in the correct rearrangement.
  • 55.0602 — dropped that same factor in the other direction.
  • 121.1 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Euler's Formula

Example 10
Euler buckling load — solve for critical load (case 4) — Euler's Formula (10)

A mechanics of materials problem uses Euler buckling load. Given modulus (E) = 18,000 ksi; moment of inertia (I) = 480.0 in⁴; effective length factor (K) = 1.8000; unbraced length (L) = 239.0 in, determine the critical load (Pcr) in kip.

Given

  • modulus(E)=18,000ksimodulus (E) = 18,000 ksi
  • momentofinertia(I)=480.0in4moment of inertia (I) = 480.0 in^{4}
  • effectivelengthfactor(K)=1.8000effective length factor (K) = 1.8000
  • unbracedlength(L)=239.0inunbraced length (L) = 239.0 in

Find

critical load (Pcr), in kip

Start with the thinking

  • The governing relation printed in this handbook section is Euler buckling load.
  • Everything except Pcr is given, so isolate Pcr symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2
  2. Step 2 — Rearrange the relation so that Pcr stands alone on the left-hand side.

  3. Step 3 — List the givens: modulus (E) = 18,000 ksi, moment of inertia (I) = 480.0 in⁴, effective length factor (K) = 1.8000, unbraced length (L) = 239.0 in.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    Pcr=460.8 kipPcr = 460.8\ \text{kip}
  6. Step 6 — Check: returning Pcr = 460.8 kip to

    Pcr=π2EI/(KL)2P_{cr} = \pi^2 E I / (K L)^2

    reproduces the given quantities, and both sides carry the same units.

Answer:
Pcr=460.8 kipPcr = 460.8\ \text{kip}

Why the other options are there

  • 921.5 — kept a factor of two that cancels in the correct rearrangement.
  • 230.4 — dropped that same factor in the other direction.
  • 506.8 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Euler's Formula

© 2026 Dr. Steve Efe. Civil Engineering Capstone Studio. All rights reserved.