Water Tank Capacity Calculator
Find the exact volume of your cylindrical or rectangular water tank in litres, cubic metres, and US gallons — just enter its dimensions.
Common Tank Sizes Reference
Typical household and farm water tank capacities for comparison.
| Common Tank Size | Typical Use |
|---|---|
| 500 L | Small household rooftop tank |
| 1,000 L | Standard household sintex-style tank |
| 2,000 L | Larger household or small farm use |
| 5,000 L | Farm storage / multiple household use |
| 10,000 L+ | Farm irrigation buffer / community storage |
How This Calculator Works
Standard geometry formulas, converted straight to litres.
Why Tank Capacity Matters
Knowing your water tank's exact capacity underpins nearly every water planning decision — from sizing a pump correctly, to scheduling irrigation cycles, to simply knowing how many days of household or livestock water you have in reserve before needing to refill. Tank capacity is printed on some commercial tanks, but many farm and household tanks are custom-built or unlabeled, making a quick, accurate calculation from basic dimensions genuinely useful.
The Two Standard Tank Volume Formulas
Cylindrical Tanks
Volume (m³) = π × (Diameter ÷ 2)² × Height
Litres = Volume (m³) × 1,000
Since most cylindrical tanks are measured by their diameter rather than radius, this calculator takes diameter directly and halves it internally before squaring.
Rectangular Tanks
Volume (m³) = Length × Width × Height
Litres = Volume (m³) × 1,000
How to Use This Calculator
- Choose your tank shape — cylindrical or rectangular.
- Choose your measurement unit — metres, centimetres, or feet.
- Enter your tank's dimensions (diameter and height for cylindrical; length, width and height for rectangular).
- Tap "Calculate Tank Capacity" to see the result in litres, cubic metres, and US gallons.
Measuring Tips for Accuracy
- Measure internal dimensions where possible. External measurements include wall thickness, which slightly overstates actual usable capacity.
- For cylindrical tanks, measure diameter at multiple points if the tank isn't perfectly uniform, and use the average.
- Measure height from the true base to the maximum fill line, not necessarily the very top rim, if there's a manufacturer-recommended maximum fill level below the brim.
- For partially filled tanks, use the current water height instead of full tank height to estimate how much water is currently stored rather than total capacity.
Sizing a Tank for Your Needs
A practical way to size a new tank is to start from your expected daily water usage and multiply it by how many days of buffer storage you want. A household using roughly 500 litres a day that wants a 4-day buffer would target around 2,000 litres of capacity, for example. Farm applications, particularly for irrigation buffering or livestock, often require substantially larger capacity and may combine multiple tanks or a farm pond alongside tank storage.
Final Thoughts
Whether you're checking an existing tank's rated capacity, sizing a new installation, or figuring out how much water you currently have in storage, converting a few simple dimensions into a reliable litre figure removes the guesswork. Bookmark this page and use it any time you're planning tank purchases, pump sizing, or water budgeting.
Frequently Asked Questions
Multiply pi (approximately 3.1416) by the radius squared (half the diameter, squared) and by the tank's height, all in the same unit, to get the volume in cubic metres, then multiply by 1,000 to convert to litres.
Multiply the length, width, and height together, keeping all three measurements in the same unit, to get the volume in cubic metres, then multiply by 1,000 to convert to litres.
One cubic metre equals exactly 1,000 litres, which is the standard conversion used for tank capacity calculations.
For total tank capacity, use the full internal height of the tank. For a partially filled tank's current volume, use only the height of the water inside, measured from the bottom to the water surface.
Yes, ideally you should measure internal dimensions rather than external dimensions, since wall thickness reduces the actual usable internal volume compared to the tank's outer measurements.
Divide the volume in litres by approximately 3.785 to get the equivalent in US gallons.
This depends heavily on your daily water usage and how many days of storage you want as a buffer — a common approach is estimating daily usage and multiplying by your desired number of storage days to arrive at a target capacity.
This calculator covers standard cylindrical and rectangular tank shapes. For irregular shapes, the most practical approach is dividing the tank into simpler geometric sections, calculating each separately, and adding the volumes together.