WaterCalcLabWater Tank Volume Calculator
Calculate exact geometry from internal dimensions for a vertical cylinder, box or sphere.
Your result
Bars compare only results in the same unit group. They are normalized, not a time-series forecast.
Planning result based on your inputs.
How this tool works
Calculate exact geometry from internal dimensions for a vertical cylinder, box or sphere.
cylinder: πr²h; box: LWh; sphere: 4πr³/3 (m³ × 1000 = L)Example calculation
The prefilled form is a worked example. Its base-unit inputs and expected outputs are shown below; use the reset button to restore it.
| Input | Example |
|---|---|
| Tank geometry | Vertical cylinder |
| Internal radius | 1 |
| Height / water depth | 2 |
| Horizontal length | 10 |
| Horizontal width | 8 |
Planning notes for this calculator
Calculate internal geometric capacity for a vertical cylinder, rectangular box or complete sphere. Use it when dimensions are known but a nominal capacity is missing or needs checking.
Choose meaningful inputs
- Tank geometry
- Select the shape that matches the interior. The sphere option is for a complete sphere, not a partly filled spherical tank.
- Internal radius
- Radius is half the internal diameter. Cylinder and sphere calculations use this value.
- Height / water depth
- For a vertical cylinder or box, enter full internal height for capacity or water depth for current geometric contents.
- Horizontal length
- For a box, measure internal length. This field does not affect the cylinder or sphere result.
- Horizontal width
- For a box, measure internal width. Walls and surrounding space are excluded.
Read the result correctly
The result is shape volume in litres; one cubic metre equals 1,000 litres. It is not automatically usable storage: inaccessible water, fittings and freeboard can reduce that amount. The cylinder model assumes a vertical axis. A partly filled horizontal cylinder needs a circular-segment calculation and is not represented by this formula.
Common mistakes to avoid
- Using diameter in the radius field makes a cylinder volume four times too large.
- External dimensions include walls and can overstate internal capacity.
A useful next step
Compare geometric capacity with the manufacturer’s usable-volume information before estimating supply duration.
Follow a worked scenario
A separate illustrative scenario; these values do not change when you edit the form above.
- A vertical cylinder with 1 m radius and 2 m height has π × 1² × 2 = about 6.283 m³.
- Multiply by 1,000 to obtain about 6,283 L geometric capacity.
Frequently asked questions
Why do some fields not change the result?
Only dimensions relevant to the selected shape enter its formula. A cylinder uses radius and height; a box uses length, width and height; a complete sphere uses radius only.
Can I enter dimensions in centimetres?
The metric length selector uses metres. Divide centimetres by 100 before entry: a 120 cm internal diameter is 1.20 m, so its radius is 0.60 m.
Continue your plan
Rainwater Tank Size Calculator
Size usable storage for a chosen rainless interval and compare annual supply with constant annual demand. Rainfall here must be annual.
Open calculator ↗Water storageRainwater Storage Duration Calculator
Divide usable storage by a constant daily demand to estimate rainless supply duration.
Open calculator ↗Water storageWater Tank Fill Time Calculator
Estimate refill time from current contents and a constant inlet flow.
Open calculator ↗Related reading
Water storageHow to Calculate Tank Capacity
Geometry tells you the volume inside a shape. Sizing asks whether that volume matches supply and demand. Establish which question you need to solve. A correctly calculated cylinder volume can still be an unsuitable garden supply. Conversely, an appropriate capacity target needs product dimensions and operating levels to confirm how much water can actually be stored.
Read guide ↗
Water storageHow to Choose a Rainwater Tank
Write a short specification describing the uses, required usable volume, outlet flow, installation space and maintenance access. A tank is one component of a system, so compare options against the same specification. A bigger container is not automatically better if it cannot be filled regularly, is difficult to service or needs a costly pump arrangement.
Read guide ↗Sources & method references
- Texas Water Development Board: Rainwater Harvesting Manual
Collection, storage and system-planning context. Geometry and unit conversions on this page are stated explicitly.
Method version 1.1 · Explanations and examples reviewed: 2026-10-11