Water Tank Capacity Calculator
Calculate rectangular or cylindrical water tank capacity in litres, cubic metres, and US gallons from internal dimensions.
Enter the tank's internal dimensions, choose its shape, and optionally set a usable fill level. The result shows gross and usable storage plus an indicative household supply duration.
Tank Dimensions
Use clear internal dimensions, not the outside size of the tank.
Volume and duration are planning estimates. Confirm structural, plumbing, waterproofing, and local requirements separately.
Compare Similar Calculators
House Construction Cost Calculator
Estimate house construction cost in India from built-up area, city tier, quality, and floors. Review per-square-foot rates plus material and labour shares.
ViewConcrete Calculator
Calculate concrete volume, cement bags, sand quantity, aggregate quantity, and material costs for slabs, foundations, columns, beams, and construction projects.
ViewStaircase Calculator
Calculate staircase steps, riser height, tread depth, total run, stair angle, and stringer length from your floor-to-floor height and available space.
ViewMore Construction Calculators
How the Water Tank Capacity Calculator Works
Choose the Tank Shape
Select a rectangular tank or a vertical cylindrical tank.
Enter Internal Dimensions
Use clear inside dimensions so wall thickness is not counted as stored water.
Set the Usable Fill
Allow for freeboard or a level below the tank's full height if needed.
Review Capacity
See gross capacity, usable litres, gallons, and estimated household duration.
Water Tank Capacity Formula
Rectangular: L × W × H; Cylindrical: π × r² × H; Litres = cubic metres × 1,000
The calculator converts every entered dimension to metres before finding volume. For a rectangular tank it multiplies internal length, width, and height. For a cylindrical tank it uses half the internal diameter as the radius. Usable capacity is gross volume multiplied by the chosen fill percentage.
Example Calculation
Input: Rectangular tank: 6 ft × 4 ft × 4 ft at 90% usable fill
Output: Gross capacity is about 2,718 litres and usable capacity is about 2,446 litres.
Common Uses
- • Sizing an overhead household tank
- • Checking an underground sump
- • Converting tank dimensions to litres
- • Estimating backup-water duration
Questions about this calculator
Use internal clear dimensions. External dimensions include the wall thickness and therefore overstate the volume available for water.
A tank may not be filled to the brim because of overflow level, freeboard, pipe position, sediment allowance, or operating practice. Adjust the fill percentage to reflect the actual maximum water level.
One cubic metre equals exactly 1,000 litres. One cubic foot is approximately 28.3168 litres.
No. It estimates liquid volume only. A qualified professional should design the structure, reinforcement, foundation, waterproofing, access, overflow, and plumbing.
How to Calculate Water Tank Capacity
Measure the clear space inside the tank. A rectangular tank uses length × width × water height. A round vertical tank uses π × radius² × water height. After converting the volume to cubic metres, multiply by 1,000 to obtain litres.
Gross Capacity and Usable Storage
Catalogue capacity often describes the tank at its full geometric volume. In practice the overflow, inlet arrangement, freeboard and minimum pump level can reduce the water you can use. The fill control lets you plan with a more realistic operating volume.
Planning Household Storage
Daily use varies substantially with household size, fixtures and habits. The duration result is only a planning comparison based on the daily litres per person you enter. Confirm local supply conditions and obtain professional advice for structural and plumbing design.
Embed this calculator
Add the Water Tank Capacity Calculator to your website for free. Keep the attribution link in the widget intact.
The embedded route is excluded from search indexing to prevent duplicate-content pages. The main calculator page remains the canonical source.
Written & maintained by Aditya Singh
Aditya Singh is a software engineer and the founder of DevCalc, based in Uttar Pradesh, India. He builds and maintains every calculator on this site using documented formulas, worked examples, and clearly stated limitations, with careful attention to accuracy. Read more about the author →