Home & Construction Calculators
Use this tank volume and fill calculator to estimate total capacity, filled volume, remaining space, gallons, liters, fluid weight, and preliminary water-storage cost.
About the Tank Volume and Fill Calculator
This tank volume calculator estimates full capacity, filled volume, remaining space, gallons, liters, fluid weight, and preliminary cost. It supports rectangular tanks and vertical cylindrical tanks using inside dimensions.
Formula and assumptions
Rectangular volume = length × width × height. Cylindrical volume = π × radius² × height, where diameter is entered as length. Convert cubic feet to U.S. gallons by multiplying by 7.48052, then multiply by 3.78541 for liters. Filled volume = full capacity × fill percentage.
Worked example
For a rectangular tank measuring 20 ft × 10 ft × 4 ft, the full capacity is about 5,984.4 gallons. At 75% fill, the active volume is about 4,488.3 gallons and the remaining space is about 1,496.1 gallons. At 8.34 lb/gal, the fluid weighs about 37,433 lb. The sample cost estimate adds fluid cost and delivery or installation.
Measurement checklist
- Measure inside length, width, diameter, and height.
- Confirm the manufacturer rated capacity.
- Reserve safe freeboard and account for overflow protection.
- Check fluid compatibility, ventilation, access, and support.
- Include pumps, pipes, fittings, delivery, and installation separately.
Manual calculation steps
- Identify the tank shape.
- Calculate cubic feet using the matching geometry.
- Convert cubic feet to gallons and liters.
- Apply the desired fill percentage.
- Calculate remaining space and fluid weight.
- Add fluid, delivery, installation, and equipment costs.
Common mistakes
- Using outside dimensions instead of inside dimensions.
- Filling to 100% when freeboard is required.
- Confusing gallons with liters.
- Ignoring tank support and fluid weight.
Frequently asked questions
How do I calculate a cylindrical tank?
Select vertical cylindrical tank, enter the inside diameter as length, and enter the inside height. The calculator uses πr²h.
Why not fill a tank completely?
Freeboard may be needed for expansion, waves, overflow control, thermal changes, and safe operation.
What does fluid density change?
Density changes the estimated weight. Water is about 8.34 lb per U.S. gallon, while other fluids may differ.
Is this a structural tank design?
No. Confirm tank rating, foundation, supports, connections, permits, and safety requirements with the manufacturer or a qualified professional.