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Tank Volume Calculator

Find full tank size in US gallons for a box tank or upright round tank from the chosen shape and inside lengths in feet.

Result

179.53 gal

A rectangular tank holds about 179.53 gallons

Quick Answer

A tank volume calculator finds cubic feet from the selected tank shape, then multiplies by 7.48052 for US gallons. A rectangular tank that is 4 feet long, 3 feet wide, and 2 feet high holds about 179.53 US gallons when filled fully to the top.

Tank Capacity Calculator Explained For Two Basic Shapes

A tank volume calculator finds the full space inside a simple tank. Pick a box tank or an upright round tank. For a box, multiply length, width, and height. For a round tank, find radius from diameter, then multiply the round end area by height. Both paths first give cubic feet. The last step changes cubic feet to US gallons. Use inside sizes because thick walls make the inner space less than the outer size. The math assumes a full tank with flat ends and a true shape. Round heads, sloped floors, baffles, pipes, and a fill gap can cut the space. This result is only a basic geometric plan check, not a rated or certified tank capacity for service.

Rectangular And Cylinder Tank Volume Formulas In Gallons

NIST lists 1 cubic foot as 7.480519 US gallons. The tool uses 7.48052. The calculation uses full internal volume, so freeboard, safe fill rules, or thermal expansion space must be removed in a separate step.

  • Rectangular cubic feet = length × width × height.
  • Cylinder radius = diameter ÷ 2.
  • Vertical cylinder cubic feet = π × radius² × height.
  • US gallons = cubic feet × 7.48052.

Using This Tank Volume Calculator In Five Clear Steps

Inputs

  • Shape: select rectangular or vertical cylindrical.
  • Length: the inside tank length in feet for a rectangular tank.
  • Width: the inside tank width in feet for a rectangular tank.
  • Height: the inside height in feet for either shape.
  • Diameter: the inside diameter in feet for a vertical cylinder.

Steps

  1. Select the tank shape.
  2. Measure the needed inside dimensions.
  3. Enter all values in feet.
  4. Read the cubic-foot volume and US gallons.
  5. Compare full volume with the tank label and safe fill rules.

Rectangular Tank Example With Gallon Conversion Shown

4 ft length, 3 ft width, and 2 ft height.

  1. Find cubic feet: 4 ft × 3 ft × 2 ft = 24 cu ft.
  2. Convert to gallons: 24 cu ft × 7.48052 = 179.53248 gal.

179.53 US gallons, rounded to two decimal places.

Vertical Cylinder Example With Radius And US Gallons

Inputs: 4 ft diameter and 3 ft height.

Step 1, find radius: 4 ft ÷ 2 = 2 ft.

Step 2, find cubic feet: π × 2² ft × 3 ft = 37.69911 cu ft.

Step 3, convert to gallons: 37.69911 cu ft × 7.48052 = 282.00896 gal.

Result: 282.01 US gallons, rounded to two decimal places.

When A Geometric Tank Capacity Estimate Helps Most

Use this tool for a first check of a box tank or upright round tank. Confirm the tank label, safe fill level, tank state, and liquid rules before use.

For nearby tools, the construction calculators hub lists every material and quantity calculator, and the glossary defines common calculator terms.

Assumptions

  • All dimensions are inside measurements in feet.
  • The tank matches the selected exact shape.
  • The cylinder stands upright with flat top and bottom.
  • The result is full geometric capacity.
  • Gallons are US liquid gallons.

Limitations

  • The result does not find partial fill volume.
  • Outside dimensions can overstate inside capacity.
  • Rounded heads, cones, slopes, and odd shapes are not included.
  • Baffles, pipes, fittings, and dead space are not removed.
  • Safe fill limits and liquid expansion need separate review.

In Practice

A common mistake is using outside sizes as though they show inner space. Use inside sizes and check the tank plate or maker's data. This result is not a rated size, code check, or safe fill limit.

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Frequently Asked Questions About Tank Volume Results

How Do You Calculate A Rectangular Tank In Gallons?

Rectangular tank gallons come from inside length multiplied by inside width and inside height. Then use 7.48052. A 4 × 3 × 2 ft tank gives 24 cu ft × 7.48052 = 179.53 US gal. Keep all three sizes in feet before multiplying.

How Do You Calculate A Vertical Cylinder Tank?

A vertical cylinder tank uses half the inside diameter as the radius in the volume formula. Divide diameter by two to find radius. Then use π × radius² × height and change cubic feet to US gallons with 7.48052. Keep the tank upright and use inside height.

Should Tank Measurements Be Taken Inside Or Outside?

Inside tank measurements give the best geometric estimate because liquid fills the inner space, not the outer shell. Outside sizes include wall thickness. Liners, baffles, and pipes can cut space even when inner wall sizes are used, so a tank plate remains the better source when available.

Does One Cubic Foot Equal 7.48052 US Gallons?

One cubic foot equals about 7.480519 US liquid gallons under the NIST conversion table. The tool uses 7.48052. Small gaps can come from rounding the factor or final answer. This factor does not convert to Imperial gallons.

Can This Calculator Find A Partly Filled Tank Volume?

This tank volume calculator finds full capacity for a box tank or an upright round tank. A part-full box can use liquid depth as height. The same method works for an upright round tank when the liquid level is known, but the displayed result should be labeled as filled volume rather than total capacity.

Sources

Last updated: . Reviewed for accuracy against the formula shown above.