Tank Volume Calculator

Frequently Asked Questions

How many gallons in a 36x18x18 aquarium?

36 x 18 x 18 = 11,664 cu in / 1728 = 6.75 cu ft x 7.481 = 50.5 gallons.

How many gallons in a 24-inch diameter by 48-inch tall vertical tank?

pi x (12)^2 x 48 / 1728 = 12.57 cu ft x 7.481 = 94.0 gallons.

How do I find the volume of a horizontal cylindrical tank?

Use the same formula as vertical but swap height for length: pi x (D/2)^2 x length / 1728 cu in per cu ft, then x 7.481 for gallons.

What is 1 cubic foot in gallons?

1 cubic foot = 7.481 US gallons. 1 gallon = 0.1337 cubic feet.

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Estimates for informational purposes only.

Important Disclaimer: Estimates for informational purposes only.

This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How This Calculator Works

Volume formulas by shape (all dimensions in inches, converted to feet internally):

Rectangular: L x W x H / 1728 cu in per cu ft

Cylindrical vertical: pi x (D/2)^2 x H / 1728

Cylindrical horizontal: pi x (D/2)^2 x L / 1728

Oval: pi x (W/2) x (H/2) x L / 1728 (approximate for elliptical cross section)

All results are then multiplied by 7.481 to convert cubic feet to US gallons. The fill percentage gives the volume at any partial fill level.

Identifying Your Tank Shape

Common tank shapes by application:

Rectangular: aquariums, oil storage IBC totes, cisterns, basement water tanks

Cylindrical vertical (upright): propane tanks, water pressure tanks, above-ground oil tanks, well pressure tanks

Cylindrical horizontal (on its side): propane trucks, underground oil tanks, fuel trailers, hot water heaters laid sideways

Oval / elliptical: RV holding tanks, boat fuel tanks, some agricultural sprayer tanks

Partial Fill Calculations

The fill percentage input lets you find the volume at any level. 100% = full tank. 50% = half full. For a 100-gallon tank at 75% fill, the fill volume is 75 gallons. This is useful for:

Calculating fuel remaining based on a gauge reading

Determining how many gallons to add to reach a target level

Checking that a partially filled tank stays within structural weight limits

Note: this calculator assumes linear fill (suitable for rectangular, vertical cylinder, and oval tanks). A horizontal cylinder does not fill linearly with depth - the relationship between depth and volume is non-linear due to the curved bottom.

FAQ

How many gallons in a 48x24x24 inch tank?

Rectangular: 48 x 24 x 24 = 27,648 cubic inches / 1728 = 16 cu ft x 7.481 = 119.7 gallons.

How many gallons in a 500-gallon propane tank?

Most residential propane tanks are horizontal cylinders. A standard 500-gallon tank measures about 10 ft long and 37.5 in diameter. Propane tanks are filled to 80% capacity for thermal expansion: 500 x 0.80 = 400 gallons maximum working capacity.

What is the volume of a 55-gallon drum?

A standard 55-gallon drum is about 23 in diameter and 34.5 in tall. Volume = pi x (11.5)^2 x 34.5 / 1728 = 7.37 cu ft x 7.481 = 55.1 gallons - consistent with the nominal size.

How do I measure an irregular tank?

For tanks that do not match the standard shapes, measure the widest and tallest cross-sections. If roughly oval, use the oval formula. For very irregular shapes, fill the tank with a known volume of water to measure capacity directly.

Tank Volume Calculator

Frequently Asked Questions

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