This free tank volume calculator gives you the tank capacity in litres, cubic metres and US gallons for three common shapes — vertical cylinder, horizontal cylinder and rectangular tanks. Enter the dimensions in millimetres, and for any cylindrical tank volume or rectangular vessel you get the full capacity instantly, plus the partial / filled volume and percentage full when you add a fill height. It works as a water tank size, storage tank, chemical vessel and process-tank litre calculator.
How to calculate tank volume
Every tank volume comes down to the cross-sectional area multiplied by the length or height, converted into a usable unit. The two core formulas are:
- Cylindrical tank:
V = π/4 × D² × H— whereDis the inside diameter andHis the height (or, for a horizontal tank, the length). - Rectangular tank:
V = L × W × H— length × width × height.
Because the calculator takes dimensions in millimetres, each value is divided by 1,000 to convert to metres before the volume is worked out, so the answer comes out in cubic metres. Then it is converted: litres = m³ × 1000 and US gallons = litres × 0.264172.
Worked example. Take a vertical cylindrical tank that is 1,000 mm in diameter and 1,500 mm tall. Convert to metres: D = 1.0 m, H = 1.5 m. Then V = π/4 × 1.0² × 1.5 = 0.7854 × 1.5 ≈ 1.178 m³. Multiply by 1,000 and the tank holds about 1,178 litres (roughly 311 US gallons) — exactly what the calculator returns when you enter those two numbers above.
Partial / horizontal tank volume
Finding how much liquid is actually in a tank depends on the shape. For a vertical cylinder or a rectangular tank, the filled volume scales directly with depth — just use the fill height in place of the full height in the same formula, and the percentage full is simply fill height ÷ full height.
A horizontal cylinder is the tricky one, because as the liquid level rises the wetted cross-section is a circular segment, not a simple fraction of the circle. The exact partial volume at a liquid depth h is:
V = L × ( r² × acos((r − h) / r) − (r − h) × √(2·r·h − h²) )
where r is the radius (D/2) and L is the length. The depth h is clamped to the range 0 to D. At h = D the segment formula resolves to the full cylinder volume, and at h = r (half full) it gives exactly half the capacity — which is why dipstick-to-litre conversions on a horizontal tank are never linear. The calculator handles all of this for you the moment you type a fill height.
Common tank sizes
These are quick reference capacities for a vertical cylindrical tank at a few standard diameter × height combinations. Use them as a sanity check against the calculator.
| Diameter × Height (mm) | Volume (m³) | Capacity (litres) |
|---|---|---|
| 1000 × 1500 | 1.178 | ~1,178 |
| 1000 × 2000 | 1.571 | ~1,571 |
| 1200 × 2000 | 2.262 | ~2,262 |
| 1500 × 2000 | 3.534 | ~3,534 |
| 1500 × 3000 | 5.301 | ~5,301 |
| 2000 × 3000 | 9.425 | ~9,425 |
| 2400 × 3600 | 16.286 | ~16,286 |
From tank sizing to inventory
A tank volume calculator answers one question. Running a plant means turning that capacity into something you act on — batch sizes, reorder points, vessel utilisation and stock value. Inside OEMup ERP the same sizing maths is built in: tank and vessel capacities feed into inventory levels, batch and production planning, and material costing, so a half-full chemical tank or water reservoir shows up as real, trackable stock instead of a number on a whiteboard. See it work end to end — start a free trial or explore the full feature set.
Frequently asked questions
How do I calculate tank volume in litres?
Work out the volume in cubic metres, then multiply by 1,000 (1 m³ = 1,000 litres). For a cylinder, V = π/4 × D² × H in metres; for a box, V = L × W × H. A 1,000 mm dia × 1,500 mm tall tank is about 1.178 m³, or about 1,178 litres. The calculator above does it as you type.
What is the formula for a cylindrical tank?
The volume of a cylindrical tank is V = π/4 × D² × H, where D is the inside diameter and H is the height (or length, for a horizontal tank). Convert millimetres to metres (÷1,000) first, so the answer is in cubic metres; multiply by 1,000 for litres or by 264.172 for US gallons.
How do I find a partially filled tank volume?
For a vertical cylinder or rectangular tank, scale by depth — use the fill height instead of the full height. For a horizontal cylinder the cross-section is a circular segment: V = L × ( r²·acos((r−h)/r) − (r−h)·√(2rh−h²) ), with r the radius and h the liquid depth. Enter a fill height and the calculator applies the right formula automatically.
How many litres is a 1000 litre tank in m³?
A 1,000 litre tank is exactly 1 cubic metre, because 1 m³ equals 1,000 litres. So 5,000 litres is 5 m³ and 500 litres is 0.5 m³. To convert litres to cubic metres, divide by 1,000; to go the other way, multiply by 1,000.
Need more shop-floor tools? Browse all free calculators, or try the Pump Power Calculator and the Pipe Weight Calculator.
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