Select the cross-section shape of your tank
ft
Please enter a positive diameter.
Internal diameter of the cylindrical tank
ft
Please enter a positive height.
Vertical height (upright) or horizontal length (lying down)
Unit used for all dimensions above
Tank Capacity
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⚠️ Disclaimer: This calculator uses internal dimensions. Always measure the inside of your tank. Actual usable capacity may be less due to fittings, vents, or installation requirements. Consult a professional for critical applications.
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Sources & Methodology
Volume formulas verified against standard engineering references. Unit conversions use NIST official values: 1 US gallon = 231 cubic inches exactly; 1 UK gallon = 277.42 cubic inches.
NIST — Unit Conversions
Official conversion factors for volume units: US gallon, UK gallon, litre, cubic metre, cubic foot
Engineering Toolbox — Tank Volume
Engineering reference for cylindrical and rectangular tank volume calculations used in industrial and residential applications
Methodology: Cylindrical tank: V = π × (d/2)² × h. Rectangular tank: V = L × W × H. Conversion: 1 ft³ = 7.48052 US gal = 6.22882 UK gal = 28.3168 L. 1 m³ = 1,000 L = 264.172 US gal = 219.969 UK gal. All input units converted to cubic metres internally before converting to output units.
⏱ Last reviewed: April 2026
Tank Volume Calculator — Gallons, Litres & m³ 2026
Calculating tank capacity is essential for water storage, fuel storage, aquaculture, heating systems, irrigation, and chemical containment. The formula depends on the tank shape — cylindrical tanks use the circle area times height, while rectangular tanks multiply the three linear dimensions. This calculator handles both, then converts to every common volume unit so you get the exact figure you need.
Key Formulas
Cylindrical: V = π × (d/2)² × h
d = internal diameter | h = height or length | Then: US gal = V(ft³) × 7.481 | Litres = V(m³) × 1,000
Rectangular: V = L × W × H
L = length | W = width | H = height | All must be in the same unit before calculating
Unit Conversion Reference Table
| Volume | US Gallons | UK Gallons | Litres | Cubic Feet |
|---|---|---|---|---|
| 1 m³ | 264.17 | 219.97 | 1,000 | 35.315 |
| 1 ft³ | 7.481 | 6.229 | 28.317 | 1 |
| 1 US gal | 1 | 0.833 | 3.785 | 0.134 |
| 1 UK gal | 1.201 | 1 | 4.546 | 0.161 |
| 1 litre | 0.264 | 0.220 | 1 | 0.0353 |
Common Tank Sizes and Their Capacities
- 275-gallon IBC tote: Approximately 48″ × 40″ × 53″ internal; holds 275 US gallons (1,041 litres).
- Standard hot water heater: 40–80 US gallons; a 40-gallon tank is roughly 18″ diameter × 59″ tall.
- Residential well pressure tank: Typically 20–44 gallons (76–167 litres) for most single-family homes.
- 1,000-gallon septic tank: Typically 8.5′ × 5.5′ × 5.5′ precast concrete; holds 3,785 litres.
- 5,000-gallon water storage: A vertical cylinder 8′ diameter and 15′ tall holds approximately 5,655 gallons — tanks slightly larger than rated capacity allow for freeboard.
Why Internal Dimensions Matter
Tank walls have thickness — typically 3–6 mm for steel tanks, 50–150 mm for concrete cisterns, and 5–25 mm for plastic tanks. Always measure from the inside surface to inside surface. The difference may seem small but can represent 5–10% of stated capacity on smaller tanks. For a 500-gallon steel tank with 6 mm walls and 48″ nominal diameter, the effective internal diameter is 47.5″, reducing actual capacity by about 2%.
💡 Water weight tip: Water weighs 8.34 lbs per US gallon (1 kg per litre). Multiply your tank capacity in gallons by 8.34 to find the weight of a full tank in pounds, or use litres directly for kilograms. A 275-gallon IBC tote full of water weighs 275 × 8.34 = 2,294 lbs of water, plus the 130 lb tote itself = 2,424 lbs total.
Frequently Asked Questions
V = pi x (diameter/2) squared x height. Use internal dimensions. For diameter 6 ft and height 8 ft: radius = 3 ft, V = 3.14159 x 9 x 8 = 226.19 cubic feet = 226.19 x 7.481 = 1,692 US gallons.
Multiply the cubic foot volume by 7.48052 for US gallons. For cubic metres, multiply by 264.172. A 5 ft diameter, 10 ft tall tank: radius = 2.5, V = pi x 6.25 x 10 = 196.35 cubic feet = 1,469 US gallons.
V (cubic feet) = length x width x height. US gallons = V x 7.48052. For 4 ft x 3 ft x 2 ft: V = 24 cubic feet = 179.5 US gallons = 679.4 litres.
In metres: litres = L x W x H x 1,000 (rectangular) or pi x r squared x h x 1,000 (cylindrical). In centimetres: divide cubic centimetres by 1,000. A 1m x 0.5m x 0.8m rectangular tank holds 400 litres.
1 US gallon = 3.785 litres. 1 UK (imperial) gallon = 4.546 litres — about 20% larger than a US gallon. A tank labelled 275 gallons in the US holds 1,041 litres; the same label in the UK would mean 1,250 litres.
Total volume = pi x r squared x L (same as vertical). Orientation does not change total capacity. However, partial-fill volume at fill depth d = L x (r squared x arccos((r-d)/r) - (r-d) x sqrt(2rd - d squared)), which requires a separate calculation for non-full tanks.
Water weighs 8.34 lbs per US gallon or 1 kg per litre. Multiply capacity in gallons by 8.34 for pounds, or capacity in litres for kilograms. A 500-gallon tank holds 500 x 8.34 = 4,170 lbs of water plus the tank's own weight.
Volume = 3 x 4 x 5 = 60 cubic feet. US gallons = 60 x 7.48052 = 448.8. UK gallons = 60 x 6.22882 = 373.7. Litres = 60 x 28.3168 = 1,699.
1,000 US gallons = 133.68 cubic feet = 3.785 cubic metres. For a cylindrical tank with 4 ft diameter (radius 2 ft): height = 133.68 / (pi x 4) = 10.63 ft. For 5 ft diameter: height = 6.81 ft. Many dimension combinations are possible.
Always use internal dimensions. Tank walls reduce the usable volume. For steel tanks subtract 2 x wall thickness from each external dimension. For concrete tanks subtract 2 x 100-150 mm. Internal dimensions give the actual fluid capacity.
Multiply cubic feet by 7.48052 for US gallons, or by 6.22882 for UK gallons. To reverse: divide US gallons by 7.48052 to get cubic feet. Example: 50 cubic feet = 374 US gallons or 311 UK gallons.
A standard 275 US gallon IBC tote measures approximately 48 x 40 x 53 inches internally. V = 48 x 40 x 53 = 101,760 cubic inches = 58.89 cubic feet = 440.5 litres x ... = approximately 1,041 litres = 275 US gallons, confirming the nominal rating.
For rectangular tanks: partial volume = full volume x (fill height / total height). For cylindrical tanks lying horizontally, use the segment formula or a tank strapping chart. Most oval and irregular tanks ship with a strapping table from the manufacturer relating depth to volume.
A tank strapping chart (or tank calibration table) maps each inch (or centimetre) of liquid depth to the corresponding volume in gallons or litres. It accounts for the exact shape, including dished ends on cylindrical tanks. Manufacturers provide these for horizontal tanks where the fill-depth to volume relationship is non-linear.
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