About this calculator
Capacity of a water, fuel or septic tank, plus how much is in it at a measured level, which matters for horizontal tanks where the level isn’t proportional.
How it’s calculated
Horizontal cylinder part-full: segment area = r² × acos((r − h) ÷ r) − (r − h) × √(2rh − h²), multiplied by length.
Worked example
With these inputs:
- Tank
- Horizontal cylinder
- Diameter
- 4 ft
- Length / height
- 8 ft
- Liquid level (optional)
- 0 in
the result is:
- Tank capacity
- 752.02 gal
- Total capacity
- 752.02 gal
Tips from the trade
- Use inside dimensions. Wall thickness matters on small tanks.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and local building codes before ordering.