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Density

Environmental Engineering · FE Reference Handbook section

Environmental Engineering
11 formulas
10 exam-style examples
~60 min
All Environmental Engineering lectures

Handbook notes for this section

Definitions and conditions exactly as the handbook states them.

  • The dry adiabatic lapse rate ΓAD is 0.98°C per 100 m (5.4°F per 1,000 ft). This is the rate at which dry air cools adiabatically
  • The actual (environmental) lapse rate Γ is compared to ΓAD to determine stability as follows:
  • Lapse Rate Stability Condition
  • Surface Wind Solar Insolation Cloudinesse
  • a. Surface wind speed is measured at 10 m above the ground.
  • b. Corresponds to clear summer day with sun higher than 60° above the horizon.
  • c. Corresponds to a summer day with a few broken clouds, or a clear day with sun 35-60° above the
  • d. Corresponds to a fall afternoon, or a cloudy summer day, or clear summer day with the sun 15-35°.

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
Density — solve for density — Density

density of a sludge sample measured in the laboratory Given mass (m) = 46.0000 kg; volume (V) = 0.5030 m^3, determine the density (rho) in kg/m^3.

Given

  • mass(m)=46.0000kgmass (m) = 46.0000 kg
  • volume(V)=0.5030m3volume (V) = 0.5030 m^3

Find

density (rho), in kg/m^3

Start with the thinking

  • The governing relation printed in this handbook section is Density.
  • Everything except rho is given, so isolate rho 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.
  • Density of a material sample is mass per unit volume, a fundamental property used throughout environmental engineering calculations.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ρ=mV\rho = \dfrac{m}{V}
  2. Step 2 — Rearrange symbolically for rho:

    ρ=mV\rho = \dfrac{m}{V}
  3. Step 3

    Listthegivens:mass(m)=46.0000kg,volume(V)=0.5030m3List the givens: mass (m) = 46.0000 kg, volume (V) = 0.5030 m^3
  4. Step 4 — Substitute the given values:

    ρ=46.00000.5030\rho = \dfrac{46.0000}{0.5030}
  5. Step 5 — Evaluate:

    \rho = 91.4513\ \text{kg/m^3}
  6. Step 6 — Check: returning rho = 91.4513 kg/m^3 to

    ρ=mV\rho = \dfrac{m}{V}

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

Answer:
\rho = 91.4513\ \text{kg/m^3}

Why the other options are there

  • 182.9 — kept a factor of two that cancels in the correct rearrangement.
  • 45.7256 — dropped that same factor in the other direction.
  • 100.6 — rounded an intermediate value before the final step.

Reference: FE Handbook — Density

Example 2
Density — solve for mass — Density (2)

density of a soil or waste material sample Given volume (V) = 0.9810 m^3; density (rho) = 1,639 kg/m^3, determine the mass (m) in kg.

Given

  • volume(V)=0.9810m3volume (V) = 0.9810 m^3
  • density(rho)=1,639kg/m3density (rho) = 1,639 kg/m^3

Find

mass (m), in kg

Start with the thinking

  • The governing relation printed in this handbook section is Density.
  • Everything except m is given, so isolate m 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.
  • Density of a material sample is mass per unit volume, a fundamental property used throughout environmental engineering calculations.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ρ=mV\rho = \dfrac{m}{V}
  2. Step 2 — Rearrange symbolically for m:

    m=ρVm = \rho V
  3. Step 3

    Listthegivens:volume(V)=0.9810m3,density(rho)=1,639kg/m3List the givens: volume (V) = 0.9810 m^3, density (rho) = 1,639 kg/m^3
  4. Step 4 — Substitute the given values:

    m=16390.9810m = 1639 0.9810
  5. Step 5 — Evaluate:

    m=1608 kgm = 1608\ \text{kg}
  6. Step 6 — Check: returning m = 1,608 kg to

    ρ=mV\rho = \dfrac{m}{V}

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

Answer:
m=1608 kgm = 1608\ \text{kg}

Why the other options are there

  • 3,216 — kept a factor of two that cancels in the correct rearrangement.
  • 803.9 — dropped that same factor in the other direction.
  • 1,769 — rounded an intermediate value before the final step.

Reference: FE Handbook — Density

Example 3
Density — solve for volume — Density (3)

density calculation from measured mass and volume of a liquid sample Given mass (m) = 781.0 kg; density (rho) = 2,648 kg/m^3, determine the volume (V) in m^3.

Given

  • mass(m)=781.0kgmass (m) = 781.0 kg
  • density(rho)=2,648kg/m3density (rho) = 2,648 kg/m^3

Find

volume (V), in m^3

Start with the thinking

  • The governing relation printed in this handbook section is Density.
  • Everything except V is given, so isolate V 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.
  • Density of a material sample is mass per unit volume, a fundamental property used throughout environmental engineering calculations.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ρ=mV\rho = \dfrac{m}{V}
  2. Step 2 — Rearrange symbolically for V:

    V=mρV = \dfrac{m}{\rho}
  3. Step 3

    Listthegivens:mass(m)=781.0kg,density(rho)=2,648kg/m3List the givens: mass (m) = 781.0 kg, density (rho) = 2,648 kg/m^3
  4. Step 4 — Substitute the given values:

    V=781.02648V = \dfrac{781.0}{2648}
  5. Step 5 — Evaluate:

    V = 0.2949\ \text{m^3}
  6. Step 6 — Check: returning V = 0.2949 m^3 to

    ρ=mV\rho = \dfrac{m}{V}

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

Answer:
V = 0.2949\ \text{m^3}

Why the other options are there

  • 0.5899 — kept a factor of two that cancels in the correct rearrangement.
  • 0.1475 — dropped that same factor in the other direction.
  • 0.3244 — rounded an intermediate value before the final step.

Reference: FE Handbook — Density

Example 4
Density — solve for density (case 2) — Density (4)

density of a sludge sample measured in the laboratory Given mass (m) = 346.0 kg; volume (V) = 0.2930 m^3, determine the density (rho) in kg/m^3.

Given

  • mass(m)=346.0kgmass (m) = 346.0 kg
  • volume(V)=0.2930m3volume (V) = 0.2930 m^3

Find

density (rho), in kg/m^3

Start with the thinking

  • The governing relation printed in this handbook section is Density.
  • Everything except rho is given, so isolate rho 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.
  • Density of a material sample is mass per unit volume, a fundamental property used throughout environmental engineering calculations.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ρ=mV\rho = \dfrac{m}{V}
  2. Step 2 — Rearrange symbolically for rho:

    ρ=mV\rho = \dfrac{m}{V}
  3. Step 3

    Listthegivens:mass(m)=346.0kg,volume(V)=0.2930m3List the givens: mass (m) = 346.0 kg, volume (V) = 0.2930 m^3
  4. Step 4 — Substitute the given values:

    ρ=346.00.2930\rho = \dfrac{346.0}{0.2930}
  5. Step 5 — Evaluate:

    \rho = 1181\ \text{kg/m^3}
  6. Step 6 — Check: returning rho = 1,181 kg/m^3 to

    ρ=mV\rho = \dfrac{m}{V}

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

Answer:
\rho = 1181\ \text{kg/m^3}

Why the other options are there

  • 2,362 — kept a factor of two that cancels in the correct rearrangement.
  • 590.4 — dropped that same factor in the other direction.
  • 1,299 — rounded an intermediate value before the final step.

Reference: FE Handbook — Density

Example 5
Density — solve for mass (case 2) — Density (5)

density of a soil or waste material sample Given volume (V) = 0.9200 m^3; density (rho) = 701.0 kg/m^3, determine the mass (m) in kg.

Given

  • volume(V)=0.9200m3volume (V) = 0.9200 m^3
  • density(rho)=701.0kg/m3density (rho) = 701.0 kg/m^3

Find

mass (m), in kg

Start with the thinking

  • The governing relation printed in this handbook section is Density.
  • Everything except m is given, so isolate m 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.
  • Density of a material sample is mass per unit volume, a fundamental property used throughout environmental engineering calculations.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ρ=mV\rho = \dfrac{m}{V}
  2. Step 2 — Rearrange symbolically for m:

    m=ρVm = \rho V
  3. Step 3

    Listthegivens:volume(V)=0.9200m3,density(rho)=701.0kg/m3List the givens: volume (V) = 0.9200 m^3, density (rho) = 701.0 kg/m^3
  4. Step 4 — Substitute the given values:

    m=701.00.9200m = 701.0 0.9200
  5. Step 5 — Evaluate:

    m=644.9 kgm = 644.9\ \text{kg}
  6. Step 6 — Check: returning m = 644.9 kg to

    ρ=mV\rho = \dfrac{m}{V}

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

Answer:
m=644.9 kgm = 644.9\ \text{kg}

Why the other options are there

  • 1,290 — kept a factor of two that cancels in the correct rearrangement.
  • 322.5 — dropped that same factor in the other direction.
  • 709.4 — rounded an intermediate value before the final step.

Reference: FE Handbook — Density

Example 6
Density — solve for volume (case 2) — Density (6)

density calculation from measured mass and volume of a liquid sample Given mass (m) = 941.0 kg; density (rho) = 2,999 kg/m^3, determine the volume (V) in m^3.

Given

  • mass(m)=941.0kgmass (m) = 941.0 kg
  • density(rho)=2,999kg/m3density (rho) = 2,999 kg/m^3

Find

volume (V), in m^3

Start with the thinking

  • The governing relation printed in this handbook section is Density.
  • Everything except V is given, so isolate V 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.
  • Density of a material sample is mass per unit volume, a fundamental property used throughout environmental engineering calculations.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ρ=mV\rho = \dfrac{m}{V}
  2. Step 2 — Rearrange symbolically for V:

    V=mρV = \dfrac{m}{\rho}
  3. Step 3

    Listthegivens:mass(m)=941.0kg,density(rho)=2,999kg/m3List the givens: mass (m) = 941.0 kg, density (rho) = 2,999 kg/m^3
  4. Step 4 — Substitute the given values:

    V=941.02999V = \dfrac{941.0}{2999}
  5. Step 5 — Evaluate:

    V = 0.3138\ \text{m^3}
  6. Step 6 — Check: returning V = 0.3138 m^3 to

    ρ=mV\rho = \dfrac{m}{V}

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

Answer:
V = 0.3138\ \text{m^3}

Why the other options are there

  • 0.6275 — kept a factor of two that cancels in the correct rearrangement.
  • 0.1569 — dropped that same factor in the other direction.
  • 0.3451 — rounded an intermediate value before the final step.

Reference: FE Handbook — Density

Example 7
Density — solve for density (case 3) — Density (7)

density of a sludge sample measured in the laboratory Given mass (m) = 903.0 kg; volume (V) = 0.5420 m^3, determine the density (rho) in kg/m^3.

Given

  • mass(m)=903.0kgmass (m) = 903.0 kg
  • volume(V)=0.5420m3volume (V) = 0.5420 m^3

Find

density (rho), in kg/m^3

Start with the thinking

  • The governing relation printed in this handbook section is Density.
  • Everything except rho is given, so isolate rho 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.
  • Density of a material sample is mass per unit volume, a fundamental property used throughout environmental engineering calculations.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ρ=mV\rho = \dfrac{m}{V}
  2. Step 2 — Rearrange symbolically for rho:

    ρ=mV\rho = \dfrac{m}{V}
  3. Step 3

    Listthegivens:mass(m)=903.0kg,volume(V)=0.5420m3List the givens: mass (m) = 903.0 kg, volume (V) = 0.5420 m^3
  4. Step 4 — Substitute the given values:

    ρ=903.00.5420\rho = \dfrac{903.0}{0.5420}
  5. Step 5 — Evaluate:

    \rho = 1666\ \text{kg/m^3}
  6. Step 6 — Check: returning rho = 1,666 kg/m^3 to

    ρ=mV\rho = \dfrac{m}{V}

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

Answer:
\rho = 1666\ \text{kg/m^3}

Why the other options are there

  • 3,332 — kept a factor of two that cancels in the correct rearrangement.
  • 833.0 — dropped that same factor in the other direction.
  • 1,833 — rounded an intermediate value before the final step.

Reference: FE Handbook — Density

Example 8
Density — solve for mass (case 3) — Density (8)

density of a soil or waste material sample Given volume (V) = 0.7660 m^3; density (rho) = 920.0 kg/m^3, determine the mass (m) in kg.

Given

  • volume(V)=0.7660m3volume (V) = 0.7660 m^3
  • density(rho)=920.0kg/m3density (rho) = 920.0 kg/m^3

Find

mass (m), in kg

Start with the thinking

  • The governing relation printed in this handbook section is Density.
  • Everything except m is given, so isolate m 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.
  • Density of a material sample is mass per unit volume, a fundamental property used throughout environmental engineering calculations.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ρ=mV\rho = \dfrac{m}{V}
  2. Step 2 — Rearrange symbolically for m:

    m=ρVm = \rho V
  3. Step 3

    Listthegivens:volume(V)=0.7660m3,density(rho)=920.0kg/m3List the givens: volume (V) = 0.7660 m^3, density (rho) = 920.0 kg/m^3
  4. Step 4 — Substitute the given values:

    m=920.00.7660m = 920.0 0.7660
  5. Step 5 — Evaluate:

    m=704.7 kgm = 704.7\ \text{kg}
  6. Step 6 — Check: returning m = 704.7 kg to

    ρ=mV\rho = \dfrac{m}{V}

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

Answer:
m=704.7 kgm = 704.7\ \text{kg}

Why the other options are there

  • 1,409 — kept a factor of two that cancels in the correct rearrangement.
  • 352.4 — dropped that same factor in the other direction.
  • 775.2 — rounded an intermediate value before the final step.

Reference: FE Handbook — Density

Example 9
Density — solve for volume (case 3) — Density (9)

density calculation from measured mass and volume of a liquid sample Given mass (m) = 981.0 kg; density (rho) = 1,018 kg/m^3, determine the volume (V) in m^3.

Given

  • mass(m)=981.0kgmass (m) = 981.0 kg
  • density(rho)=1,018kg/m3density (rho) = 1,018 kg/m^3

Find

volume (V), in m^3

Start with the thinking

  • The governing relation printed in this handbook section is Density.
  • Everything except V is given, so isolate V 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.
  • Density of a material sample is mass per unit volume, a fundamental property used throughout environmental engineering calculations.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ρ=mV\rho = \dfrac{m}{V}
  2. Step 2 — Rearrange symbolically for V:

    V=mρV = \dfrac{m}{\rho}
  3. Step 3

    Listthegivens:mass(m)=981.0kg,density(rho)=1,018kg/m3List the givens: mass (m) = 981.0 kg, density (rho) = 1,018 kg/m^3
  4. Step 4 — Substitute the given values:

    V=981.01018V = \dfrac{981.0}{1018}
  5. Step 5 — Evaluate:

    V = 0.9637\ \text{m^3}
  6. Step 6 — Check: returning V = 0.9637 m^3 to

    ρ=mV\rho = \dfrac{m}{V}

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

Answer:
V = 0.9637\ \text{m^3}

Why the other options are there

  • 1.9273 — kept a factor of two that cancels in the correct rearrangement.
  • 0.4818 — dropped that same factor in the other direction.
  • 1.0600 — rounded an intermediate value before the final step.

Reference: FE Handbook — Density

Example 10
Density — solve for density (case 4) — Density (10)

density of a sludge sample measured in the laboratory Given mass (m) = 376.0 kg; volume (V) = 0.1250 m^3, determine the density (rho) in kg/m^3.

Given

  • mass(m)=376.0kgmass (m) = 376.0 kg
  • volume(V)=0.1250m3volume (V) = 0.1250 m^3

Find

density (rho), in kg/m^3

Start with the thinking

  • The governing relation printed in this handbook section is Density.
  • Everything except rho is given, so isolate rho 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.
  • Density of a material sample is mass per unit volume, a fundamental property used throughout environmental engineering calculations.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ρ=mV\rho = \dfrac{m}{V}
  2. Step 2 — Rearrange symbolically for rho:

    ρ=mV\rho = \dfrac{m}{V}
  3. Step 3

    Listthegivens:mass(m)=376.0kg,volume(V)=0.1250m3List the givens: mass (m) = 376.0 kg, volume (V) = 0.1250 m^3
  4. Step 4 — Substitute the given values:

    ρ=376.00.1250\rho = \dfrac{376.0}{0.1250}
  5. Step 5 — Evaluate:

    \rho = 3008\ \text{kg/m^3}
  6. Step 6 — Check: returning rho = 3,008 kg/m^3 to

    ρ=mV\rho = \dfrac{m}{V}

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

Answer:
\rho = 3008\ \text{kg/m^3}

Why the other options are there

  • 6,016 — kept a factor of two that cancels in the correct rearrangement.
  • 1,504 — dropped that same factor in the other direction.
  • 3,309 — rounded an intermediate value before the final step.

Reference: FE Handbook — Density

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