Craft Quantities
Plan & Takeoffs

Measurements & Conversions

Cubic Feet to Gallons Calculator

Convert a volume in cubic feet into US gallons — for tank capacity, pond volume and water storage.

  • Answers as you type
  • Every formula cited
  • Calculated in your browser
SettingsSettings for this calculationUS
Market
Imperial · sales tax
The volume in cubic feet.

For a rectangular tank this is length × width × depth in feet. For a cylinder it is π × radius² × height. Measure to the working water level, not to the rim — the last few inches of a tank are usually freeboard you never fill.

Volume

74.81 US gallons

High confidence

1 US gallon = 231 in³ exactly, so 1 ft³ = 1728 / 231 ≈ 7.4805 gallons. Exact by definition — the only uncertainty is in your measurement of the vessel, not in the conversion.

Volume entered
10 ft³
Imperial gallons (UK)
62.29 imp gal
Litres
283.17 L
Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

  • NIST Handbook 44, Appendix C — 1 US liquid gallon = 231 cubic inches (exact)
  • 1 imperial gallon = 4.54609 L (exact), Weights and Measures Act 1985 (UK)

Inputs used

Volume (ft³)
10

Intermediate steps

Volume entered
10 ft³
Imperial gallons (UK)
62.29 imp gal
Litres
283.17 L
Final result74.81 US gallons

Confidence note: 1 US gallon = 231 in³ exactly, so 1 ft³ = 1728 / 231 ≈ 7.4805 gallons. Exact by definition — the only uncertainty is in your measurement of the vessel, not in the conversion.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-08-26 · in the site-wide review of 2026-09-06 · v1.0.0

Regulatory standards & verification citations2
  1. NIST Handbook 44, Appendix C — 1 US liquid gallon = 231 cubic inches (exact)
  2. 1 imperial gallon = 4.54609 L (exact), Weights and Measures Act 1985 (UK)
Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Tank and vessel capacity is specified in gallons and measured in feet, which means this conversion sits between the tape measure and the order. It is the step where a pond liner, a rainwater butt or a plant room tank stops being a shape and becomes a number you can buy against.

Called something else where you work? Gallon — the term in each market, how close the equivalence really is, and the standard that governs it.

How to calculate cubic feet to gallons in 2 steps

  1. Volume (ft³)The volume in cubic feet.
  2. VolumeThe tool computes the volume from those figures and shows the formula, its sources, and a confidence rating alongside it.

Cubic Feet to Gallons at common values

Page defaults, not your figures above.

Volume (ft³)Volume (US gallons)
17.48
215
537.4
1074.8
20150
50374
100748

Frequently asked questions

Is this a US gallon or an imperial gallon?
The headline figure is US gallons, which is what tank and pump capacities are quoted in across North America. The imperial equivalent is shown in the breakdown — it is about 20% larger, so mixing the two undersizes a UK tank by a fifth.
How do I get cubic feet from a round tank?
Multiply π by the radius squared by the height, all in feet. A 6 ft diameter tank has a 3 ft radius, so π × 9 × height. Use the internal diameter, not the outside — on a thick-walled tank the difference is several percent of the volume.
Does this work for gas?
As a geometric volume, yes. As a quantity of gas, no — gas volume depends on pressure and temperature, so a cubic foot of propane at tank pressure is very much more than a cubic foot at atmospheric. Gas is bought by mass or by energy content for that reason.
Why does my tank hold less than this says?
Almost always freeboard. Tanks are rarely filled to the brim, and a stated capacity is usually the working volume rather than the geometric one. Baffles, internal fittings and a domed base all take their share too.
Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.