Tank capacity
Liquid Volume of a Cylinder Calculator
Full or partial capacity for an upright cylindrical tank — read it in gallons or litres and see how much is left to fill.
This liquid volume of a cylinder calculator does more than a plain volume: it shows full capacity, the current liquid volume at the height you enter, and the empty space remaining, so you can see exactly where a tank stands.
A storage tank raises a slightly different question from a plain solid: you rarely want the total volume, you want how much is in it now and how much more it will take. That means working from the liquid height, not just the tank height, and keeping an eye on the headspace at the top.
The formula behind it
The volume of a cylinder is:
V = π r² hA worked example
Worked example. Take a cylinder with a diameter of 15 cm (so a radius of 7.5 cm) and a height of 30 cm. The base area is π × 7.5² = 176.71 cm², and multiplying by the height gives a volume of about 5.30 litres (5,301 cm³ · 1.40 US gallons).
| Unit | Equal to |
|---|---|
| 1 US gallon | 231 in³ · 3.785 L |
| 1 Imperial gallon | 277.42 in³ · 4.546 L |
| 1 cubic foot | 7.481 US gal · 28.32 L |
| 1 litre | 0.264 US gal · 0.220 Imp gal |
| 1 US gallon | 128 US fl oz |
The figure is the geometric capacity. Usable capacity is a little lower once you allow for fittings and the headspace you leave at the top, so treat it as a close upper bound.
Conversions use standard factors: 1 US gallon = 231 in³, 1 Imperial gallon = 4.54609 L, 1 litre = 1000 cm³.
How the calculation works
- Measure the tank's inside diameter and halve it for the radius.
- Measure the current liquid height inside the tank.
- The tool computes V = π r² h for the liquid volume.
- Compare it with the full capacity to see how full the tank is.
Getting an accurate measurement
Measure the inside diameter and the liquid height for a true capacity. Keep every measurement in the same system, and let the tool convert between units for you.
What people work out next
To save you a second search, here are the related answers people most often want straight after this calculation:
How much will it take to fill?
The result lists the empty space remaining in your chosen unit, and that is exactly how much you need to order to bring the tank up to the height you entered as full.
Is this the usable capacity?
It is the geometric capacity from your inside dimensions. Real usable volume is a little lower once you allow for the outlet height, fittings and the headspace left at the top.
What about a tank lying on its side?
Upright tanks fill evenly; horizontal ones do not. If your tank is on its side, switch to the horizontal-tank mode so a dip depth is converted correctly rather than treated as a simple fraction.
How full is the tank right now?
Enter the current liquid height and the calculator shows the volume held, the full capacity and the percentage full, so you can decide at a glance whether a delivery is needed.
Where people go wrong
The usual overestimate comes from measuring the outside and ignoring headspace. For a live reading use the current liquid height, not the tank's full height, and remember the geometric figure is a maximum — fittings and the gap at the top mean the usable amount is a little less.
Reading and converting your result
One number, many units. Whatever you enter, the result lists the same volume as litres, US gallons, Imperial gallons, millilitres, cubic centimetres, cubic inches, cubic feet, cubic yards and cubic metres at the same time. You almost never have to convert by hand: read the figure in the unit your job uses and copy any of the others straight from the breakdown. If you need a shareable version, the copy-link button preserves your exact inputs so a colleague opens the page with the same calculation already filled in.
Keep going
Once you have your answer you may also want to work in gallons horizontal tank litres & liters. These related calculators pick up where this one leaves off:
Where people use this
A few of the jobs it gets used for:
- Reading how full a vertical storage tank is
- Ordering the right delivery to top a tank up
- Monitoring a chemical or water tank on site
- Planning irrigation storage on a farm
The bottom line: with the radius or diameter and the height, the volume follows immediately, and the breakdown lets you hand the same number to anyone in the unit they prefer. Measure inside dimensions for anything that holds liquid, leave a little headspace at the top of a real container, and treat the geometric figure as a clean maximum rather than the final word on usable capacity.
Frequently asked questions
What is the formula for the volume of a cylinder?
V = π r² h — the area of the circular base (π r²) multiplied by the height (h). If you have the diameter instead of the radius, halve it first: r = d ÷ 2.