How to use the Water Volume Calculator
Start with Shape / system, enter the dimensions shown for that mode, and click Calculate. The result includes the formula, converted inputs, intermediate rows, and capacity in US gallons, UK (imperial) gallons, liters, cubic feet, cubic yards, and cubic meters.
- Choose a model from Shape / system.
- Enter the displayed dimensions and select each input unit.
- Set Fill level (%), Liquid depth, or the rainwater fields shown for that mode.
- Choose a Preferred capacity unit and click Calculate.
- Review the formula and assumptions, then use Copy result or Download result (.txt).
Water tank volume calculator modes
Shape / system changes the inputs for the selected setup. Cylindrical tank (vertical) and Rectangular / square tank use Fill level (%). Horizontal cylindrical tank uses Liquid depth for a partial fill. Pool (rectangular, constant or two-depth) averages Shallow-end depth and Deep-end depth. Pond (irregular - average dimensions) uses Average length, Average width, and Average depth. Septic tank (rectangular or cylindrical) adds Tank shape. Rainwater harvesting (roof runoff) uses Roof footprint area, Rainfall depth, and Runoff coefficient.
With the default values in the vertical tank mode, the result is:
Shape / system: Cylindrical tank (vertical)
Inside diameter: 4 ft
Height: 6 ft
Fill level (%): 100
Result: 75.398 cu ft, 564.1 US gal, 2.136 cu mInput units and shape assumptions
Length fields accept ft, in, yd, m, or cm. Roof footprint area accepts sq ft or sq m. Rainfall depth accepts in or mm. Enter inside liquid-holding dimensions. For a pool, put the shallow and deep measurements in their matching fields. The calculation uses those values as entered.
Rainwater harvesting uses the horizontal roof footprint. Sloped roof surface area is excluded. Its formula is Harvested volume = Roof area x Rainfall depth x Runoff coefficient. The pond result uses an elliptical-basin approximation based on Average length, Average width, and Average depth.
Water volume calculator limits
Every dimension, area, and rainfall value must be greater than zero. Fill level (%) accepts 0 through 100; Runoff coefficient accepts 0.05 through 1. A horizontal Liquid depth above the inside diameter uses the diameter as the calculation depth. In septic cylindrical mode, Width (rectangular only) still needs a positive value even though the formula ignores it.
The result is a geometric volume estimate. It does not determine septic sizing, drainage, sanitation, structural requirements, permits, or code compliance. The page script processes the calculation values in your browser. Its code contains no fetch, XMLHttpRequest, sendBeacon, or form submission for those values.
Where water volume calculations come up
- Use Cylindrical tank (vertical) or Rectangular / square tank when Fill level (%) is part of the result.
- Use Pool (rectangular, constant or two-depth) when the pool has Shallow-end depth and Deep-end depth fields.
- Use Rainwater harvesting (roof runoff) when the inputs are Roof footprint area, Rainfall depth, and Runoff coefficient.
When another construction calculator fits better
Use this page for water capacity or roof runoff. For tanks, ponds, pools, and rainwater collection alongside other material estimates, open Construction Materials Calculator. Choose Concrete Calculator for concrete volume and bag count. Use Asphalt Calculator for asphalt tonnage. The Construction Calculators for Materials, Dimensions, and Loads page groups these tools with the other construction calculators.
Frequently asked questions
How do I calculate water volume in a tank?
Choose Cylindrical tank (vertical) or Rectangular / square tank, enter the inside dimensions and Fill level (%), then click Calculate. The result includes the formula, converted values, and volume at that fill level.
How do I calculate water volume in a horizontal tank?
Choose Horizontal cylindrical tank, enter Inside diameter, Length, and Liquid depth, then click Calculate. The calculator uses a circular-segment formula for the filled portion. A depth above the diameter uses the diameter.
How does a rainwater harvesting calculator estimate runoff?
Choose Rainwater harvesting (roof runoff) and enter the horizontal Roof footprint area, Rainfall depth, and Runoff coefficient. The calculation multiplies the three converted values.
Does the water volume calculator upload my measurements?
The page script processes the calculation values in your browser. The calculator code contains no fetch, XMLHttpRequest, sendBeacon, or form submission for those values.