Tank capacity
Volume of Cylindrical Tank 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 volume of cylindrical tank 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.
The maths in one line
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
The figure above is usually the start, not the finish. These are the questions that tend to come next, answered here so you do not have to run another search:
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.
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.
Common mistakes to avoid
Keep two things straight: inside dimensions for a true capacity, and liquid height rather than tank height for how much is in there now. The full-capacity number is an upper bound, not the usable volume.
Reading and converting your result
Because volume units are where most errors creep in, the tool does the converting for you. Enter your measurements once and every common unit appears together, from millilitres up to cubic metres and across to US and Imperial gallons. Pick whichever the task calls for and lift the rest from the list; nothing needs a second calculation. The result also updates live as you change a measurement, so you can compare two sizes quickly without starting over.
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:
Common uses
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.
Good to know
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.