Tank Volume Calculator
Work out the capacity of a cylindrical or rectangular tank in gallons, litres and cubic feet — then carry the figures straight into a quote request.
Tank dimensions
Most tanks are not run completely full. Drop this to allow for freeboard, expansion or a distributor.
Estimated capacity
Enter your tank dimensions and the capacity will appear here.
Need this tank built?
Swhift builds stock and custom tanks in this size range. Send us the figures and we will quote it.
Request a QuoteThese figures are estimates
The calculator works out internal geometric volume from the dimensions you enter. It does not account for dished or domed heads, wall thickness, internal coils, baffles, distributors or required freeboard — all of which change usable capacity. Final specifications should always be confirmed with Swhift before you order.
How the numbers are worked out
For a cylinder, volume is π × radius² × length. For a rectangular tank it is simply width × height × length. Both give a result in cubic units, which is then converted: one US liquid gallon is exactly 231 cubic inches.
The weight figure assumes water at roughly 8.34 lb per gallon. If you are storing something denser than water — a glycol mix, a brine, a process liquid — the real load will be higher, and that matters for the floor as much as for the tank.
Everything here runs in your browser. Nothing is sent anywhere and nothing is stored.
Useful conversions
| From | To | Multiply by |
|---|---|---|
| Cubic inches | US gallons | ÷ 231 |
| US gallons | Litres | × 3.7854 |
| Cubic feet | US gallons | × 7.4805 |
| US gallons | Imperial gallons | × 0.8327 |
| US gallons of water | Pounds | × 8.34 |
Got a number? Here is what to do with it
Check the pressure tank chart
Stock diameters from 9-5/8 in. to 60 in. with capacity listed for every length. A stock size is normally the cheapest route.
OpenCheck the rectangular chart
55 to 3,231 gallons in published sizes — useful when the tank has to fit a room rather than the other way round.
OpenRead the sizing guide
How to get from a required volume to dimensions that will actually fit through your door.
Open
Calculator questions
How accurate is this calculator?
The arithmetic is exact for a perfect cylinder or box, but a real tank is not either of those. Dished or domed heads, wall thickness, internal coils, baffles and required freeboard all change usable capacity, usually by a few percent. Treat the result as a sizing figure, not a fill specification.
Should I use inside or outside dimensions?
Inside, if you know them. Capacity is set by internal volume, so using outside dimensions will overstate it — by more on a heavy-gauge tank than a light one. If you only have outside dimensions, tell us and we will account for the wall thickness.
Why does the fill level slider matter?
Very few tanks run completely full. Storage tanks need freeboard, hot water tanks need room for expansion, and softener vessels need space above the resin bed. Setting a realistic fill level gets you closer to the tank size you actually need to order.
What is a US gallon in this calculator?
231 cubic inches, which is the US liquid gallon. If you work in imperial gallons, the figure here will read about 20% higher than the equivalent imperial number, so use the litre value instead.
Can Swhift build the size I have calculated?
Very likely. Our stock cylindrical range runs from about 8 gallons up to roughly 1,913 gallons, and rectangular tanks go from 55 to 3,231 gallons. Anything between those, or outside them, gets quoted as a custom build.
Start a project
Have your dimensions? Let's price it
Send the figures through and we will tell you whether a stock size covers it or whether it needs a custom build.
Consultations are free. Every project is managed by a single production manager, so you talk to the person who knows your job.