Tank gauges and dipsticks read a liquid level, but you want to know how much liquid is in the tank. For upright tanks the volume is proportional to the level; for horizontal cylinders and capsules it is not, because the tank is narrower near the top and bottom. This calculator handles the common shapes of water tanks, fuel tanks, silos and hoppers.
How to use the Tank Volume Calculator
- Tank shape
- Diameter (frustum: top diameter)
- Bottom diameter (frustum)
- Length (cylinder part)
- Width
- Height (cylinder part)
- Cone height
- Liquid level (from bottom)
- Every result field is editable: type into Filled volume and Liquid level (from bottom) plus every other field update to match.
Results update as you type, and every field accepts the units shown in its menu.
How it works
Choose the tank shape, enter its dimensions and the height of the liquid measured from the bottom. The calculator returns the total capacity, the filled volume, the percentage full and the weight of water at that level.
Tips for an accurate estimate
- Measure inside dimensions of tanks and pools – wall thickness can change the volume noticeably.
- Use the average depth for pools with a sloping floor.
- Remember the weight: water weighs about 8.34 lb per US gallon (1 kg per litre), so large volumes need solid support.
- Check whether a figure is in US gallons, imperial gallons or litres before ordering chemicals or equipment.
Common mistakes to avoid
- Using wall height instead of water depth for above-ground pools.
- Assuming a horizontal tank’s volume is proportional to the liquid level – it is not.
- Mixing up flow units such as GPM, GPH and litres per minute.
Inputs explained
| Field | What to enter |
|---|---|
| Tank shape | Choose one: Vertical cylinder, Horizontal cylinder, Rectangular, Horizontal capsule … |
| Diameter (frustum: top diameter) | Units: ft, m, in, yd, cm |
| Bottom diameter (frustum) | Units: ft, m, in, yd, cm |
| Length (cylinder part) | Units: ft, m, in, yd, cm |
| Width | Units: ft, m, in, yd, cm |
| Height (cylinder part) | Units: ft, m, in, yd, cm |
| Cone height | Units: ft, m, in, yd, cm |
| Liquid level (from bottom) | Units: ft, m, in, yd, cm |
What each result means
- Percent full = [Filled volume]÷[Total volume]×100
- Weight of water at this level = [Filled volume]×1000
Example values
How the main result changes when Liquid level changes and everything else stays at the example values above:
| Liquid level (from bottom) (ft) | Filled volume (US gal) |
|---|---|
| 2 | 188 |
| 3 | 282 |
| 4 | 376 |
| 5 | 470 |
| 6 | 564 |
| 8 | 564 |
Formula
Vertical cylinder: V = π r² hHorizontal cylinder: V = L × [r² acos((r − h)/r) − (r − h)√(2rh − h²)]Capsule: cylinder + sphere cap π h² (3r − h)/3Cone bottom: π (r h/hc)² h/3 below the cone heightFrustum: π h/3 × (r₁² + r₁r₂ + r₂²)Worked example
Inputs — Tank shape: Vertical cylinder; Diameter (frustum: top diameter): 4 ft; Bottom diameter (frustum): 2 ft; Length (cylinder part): 8 ft; Width: 4 ft; Height (cylinder part): 6 ft; Cone height: 2 ft; Liquid level (from bottom): 4 ft.
Results — Total volume = 564 US gal; Total height = 6 ft; Filled volume = 376 US gal; Percent full = 66.7 %; Weight of water at this level = 3,138 lb.
Frequently asked questions
How do I calculate the volume of a cylindrical tank?
π × radius² × height for an upright tank. A 4 ft × 6 ft tank holds 75.4 ft³ = 564 gallons.
Why is a horizontal tank at half height exactly half full but not at quarter height?
The cross-section is a circle, so the bottom quarter of the height holds only about 19.6% of the volume.
How do I convert cubic feet to gallons?
Multiply by 7.48 (U.S. gallons) or 6.23 (imperial gallons).
What formula does the Tank Volume Calculator use?
Vertical cylinder: V = π r² h.