Tank capacity
Tank Cylinder Volume 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 tank cylinder volume 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.
Tanks are where geometry meets logistics. The number you act on is the gap between full capacity and the current level, because that is what you order — so a good tank calculation gives you both figures side by side, not just one.
How the volume is worked out
The volume of a cylinder is:
V = π r² hA worked example
Worked example. Take a cylinder with a diameter of 10 cm (so a radius of 5 cm) and a height of 25 cm. The base area is π × 5² = 78.54 cm², and multiplying by the height gives a volume of about 1.96 litres (1,963 cm³ · 0.52 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.
Using the calculator
- 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.
Follow-on questions, answered
To save you a second search, here are the related answers people most often want straight after this calculation:
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.
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.
What to watch out for
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.
One result, every unit
Showing every unit at once is about speed and safety: you see the answer in litres, gallons and cubic feet side by side, so there is no chance of applying the wrong conversion factor. Change the output unit at the top to make any of them the headline figure, switch the precision to exact if you want the value in terms of pi, and use copy-result to paste a tidy summary wherever you need it.
What to work out next
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:
When this comes in handy
People reach for this in a range of situations:
- 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
In short: measure the width and the height, keep them in the same unit, and the tool turns them into a volume you can read in litres, gallons, cubic feet or anything else, with the working shown so you can trust it. If a result ever looks off, re-enter the measurement you are least sure of, or switch to the diameter input and let the tool halve it for you, which catches the most common error before it matters.
Questions people ask
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.