📖 How To Use
How to Use This Circular Tank Volume Calculator
Getting your circular tank's exact capacity takes less than 30 seconds:
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Enter the diameter or radius
Measure straight across the widest point inside the tank for diameter, or from the centre to the inner wall for radius. You only need one of the two — enter whichever is easier to measure, and leave the other blank.
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Enter the height
Measure from the inside bottom of the tank to the maximum water level (usually the overflow or inlet). Use internal measurements only — wall thickness overstates volume.
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Choose your units
Each field has its own unit selector: ft, in, cm, m, or mm. You can use different units per field — the calculator converts everything internally before computing.
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Set the fill level (optional)
Drag the slider to calculate volume at a partial fill — useful for estimating current water level or planning for operational headspace. Leave at 100% for full capacity.
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Hit Calculate
Results appear instantly: litres, US gallons, UK gallons, cubic metres, cubic feet, cubic inches, and water weight in kg and lbs. Use the Copy or Print buttons to save them.
Tip: For tanks with a tapered or domed base, calculate only the cylindrical section using the straight-sided height. Add the conical base volume separately using our Cone Bottom Tank Calculator.
📐 The Formula
Circular Tank Volume Formula
A circular (cylindrical) water tank has a circular cross-section. The volume is the area of that circle multiplied by the height:
Volume = π × r² × Height
where r = radius (half the diameter)
Litres (cm inputs): V (L) = π × r² × H ÷ 1,000
Cubic metres (m inputs): V (m³) = π × r² × H
Cubic feet (ft inputs): V (ft³) = π × r² × H
This calculator converts all inputs to centimetres internally, so mixed-unit inputs always produce correct results. π is used at full machine precision (3.14159265358979…).
Diameter vs. Radius
Most tape measures give you a diameter (the full width). The calculator accepts either. Internally, radius = diameter ÷ 2. Enter one or the other — you don't need both.
Unit Conversion Reference
| Unit | Equals Litres | From Litres |
|---|
| 1 Litre (L) | 1 L | × 1 |
| 1 Cubic Metre (m³) | 1,000 L | ÷ 1,000 |
| 1 US Gallon | 3.785 L | ÷ 3.785 |
| 1 UK Gallon | 4.546 L | ÷ 4.546 |
| 1 Cubic Foot (ft³) | 28.317 L | ÷ 28.317 |
| 1 Cubic Inch (in³) | 0.01639 L | × 61.024 |
Water Weight
1 litre of fresh water = 1 kg (or 2.2046 lbs). This is the standard used for structural load calculations worldwide.
Weight (kg) = Volume (litres) × 1
Weight (lbs) = Volume (litres) × 2.2046
📏 Reference Data
Standard Circular Tank Sizes
Common circular water tank dimensions and their calculated volumes using V = π × r² × H:
| Capacity | Diameter (cm) | Height (cm) | Litres | US Gal | Full Weight |
|---|
| 250 L | 65 | 75 | 249 | 66 | 249 kg |
| 500 L | 80 | 100 | 503 | 133 | 503 kg |
| 750 L | 95 | 106 | 751 | 198 | 751 kg |
| 1,000 L | 100 | 128 | 1,005 | 265 | 1,005 kg |
| 1,500 L | 120 | 133 | 1,508 | 398 | 1,508 kg |
| 2,000 L | 130 | 151 | 2,004 | 529 | 2,004 kg |
| 5,000 L | 180 | 197 | 5,009 | 1,322 | 5,009 kg |
| 10,000 L | 230 | 241 | 10,013 | 2,645 | 10,013 kg |
Note: Actual manufacturer dimensions vary. Always verify against the supplier's data sheet and use internal dimensions.
🏗️ Use Cases
When to Use a Circular Tank Volume Calculator
Household Rooftop Tanks
Most residential poly tanks in South Asia, Africa, and Australia are circular. Before purchasing a tank or installing it on a roof, verify the volume matches your household's daily demand — typically 100–200 litres per person per day — and confirm the structure can handle the water weight. Use our Rooftop Load Bearing Calculator for the structural check.
Underground Water Storage
Buried circular cisterns for rainwater harvesting or backup supply are common in dry regions. Knowing the exact volume helps size the inlet pipe, overflow, and pump correctly. Pair this tool with our Underground Tank Volume Calculator for additional guidance.
Agricultural and Irrigation Use
Round tanks are standard in farm settings — from small drip-irrigation buffers to multi-thousand-litre sump tanks. Accurate volume figures help calculate how many irrigation cycles a full tank can support.
Industrial Process Tanks
Circular cross-sections are structurally efficient at large scale. Chemical dosing, treatment, and holding tanks in commercial settings are typically cylindrical. This tool gives volume in all common units for process design documents and regulatory filings.
Emergency Water Storage Planning
FEMA and WHO recommend at least 1 gallon (3.78 L) per person per day for emergencies. Use this calculator to verify your circular storage tanks meet the minimum 72-hour supply requirements for your household or facility.
❓ FAQ
Frequently Asked Questions
How do I calculate the volume of a circular water tank?
Multiply π (3.14159) by the radius squared, then multiply by the height: V = π × r² × H. If measuring in centimetres, divide by 1,000 to get litres. This calculator handles all unit conversions and the π constant automatically — just enter diameter or radius and height.
Should I enter the diameter or the radius?
Enter whichever is easier to measure. Diameter is the full width straight across the tank; radius is half that. Most tape measures give diameter. This calculator accepts either — enter one and leave the other blank. Entering both is fine too; the diameter field takes priority if both are filled.
What is the difference between a circular tank and a cylindrical tank calculator?
They are the same calculation. A circular tank refers to a tank with a circular (round) cross-section viewed from above, which is the same shape as a cylinder. Both use V = π × r² × H. A cylindrical tank calculator is identical — the terminology varies by region and context.
How do I measure the diameter of a tank that is already installed?
For an accessible tank, measure straight across the inside at the widest point. For a sealed installed tank, measure the outside diameter with a tape measure and subtract twice the wall thickness (typically 5–15 mm for polyethylene tanks) to get the internal diameter. Alternatively, measure the circumference with a tape and divide by π (3.14159) to get the external diameter, then subtract wall thickness.
How heavy is a full circular water tank?
Water weighs 1 kg per litre. A full 1,000-litre circular tank holds 1,000 kg of water, plus the tank shell (typically 25–55 kg for polyethylene). Always confirm your roof or stand can handle the total weight. Use our Water Tank Weight Calculator for complete load figures including the tank body.
Can I use this calculator for horizontal circular tanks?
This calculator is designed for vertical circular (upright cylinder) tanks. For tanks lying on their side, the fill calculation is different because the water cross-section changes with fill level. Use our Horizontal Tank Volume Calculator for those cases.
What is the difference between US gallons and UK gallons?
A US gallon equals 3.785 litres; a UK (Imperial) gallon equals 4.546 litres — about 20% larger. If you're in the UK, Canada, or Australia and see "gallons" on a tank label, it likely means Imperial gallons. This calculator shows both simultaneously so you can use the correct figure for your region.
How many litres does a 1-metre diameter, 1-metre tall circular tank hold?
Using V = π × r² × H: radius = 0.5 m, so V = 3.14159 × 0.25 × 1 = 0.7854 m³ = 785.4 litres. Weighing 785 kg when full, this is a typical mid-sized rooftop tank. Enter these numbers into the calculator above to confirm and see all unit conversions at once.