Water Storage & Tank Volume calculator
Calculate rectangular or cylindrical water tank capacity, partial fill, usable litres, household storage days, tanker or fill requirements, and global volume conversions.
Interactive calculator
Choose one task. Tank modes calculate shape and partial fill, while the planning modes turn known litres into family days or whole deliveries.
What to do next
Formula, example, assumptions, and FAQs — open any section for the detail.
Rectangular volume = length × width × height · Vertical cylinder = π × radius² × heightAll dimensions are converted to metres first. Cubic metres are then converted to litres using 1 m³ = 1,000 L. Use inside dimensions when possible.
Full volume = πr²L · Segment area = r² arccos((r − h) ÷ r) − (r − h)√(2rh − h²) · Filled volume = segment area × lengthFor a horizontal cylinder, water depth does not change volume linearly except at key points. Zero depth is empty, half the diameter is half full, and depth equal to diameter is full.
1 m³ = 1,000 L · 1 ft³ = 28.316846592 L · 1 US gal = 3.785411784 L · 1 UK gal = 4.54609 L · Usable = selected volume × usable%US gallons and UK gallons are different. The usable-water percentage can allow for outlet level, float shut-off, cleaning reserve, and practical tank shape differences.
Usable after reserve = capacity litres × (1 − reserve% ÷ 100) · Daily use = family members × litres/person/day · Days = usable ÷ daily useFor family planning, daily water use matters more than capacity alone. Change the daily-use input to reflect the household rather than treating the default as a guarantee.
Fills needed = ceiling(required amount ÷ fill size) · Extra capacity = fills × fill size − required amount · Cost = fills × price per fillThe count rounds up because a fraction of a standard fill may still require another delivery. Actual tanker size, billing method, and price vary by supplier and city.
A rectangular tank has inside dimensions of 1 m × 1 m × 1 m. A four-person household plans at 135 litres per person per day with a 5% reserve. A separate delivery plan needs 5,000 litres using 1,200-litre fills.
Calculation:Tank capacity: 1 × 1 × 1 = 1 m³ = 1,000 L. At 95% usable, estimated available water is 950 L. Family use is 4 × 135 = 540 L/day, so 950 ÷ 540 = 1.76 days. Delivery count is ceiling(5,000 ÷ 1,200) = 5 fills.
Result:The tank holds about 1,000 litres geometrically and about 950 litres under the 95% usable assumption. That may last the example family about 1.8 days. Five 1,200-litre fills provide 6,000 litres of capacity, 1,000 litres above the requirement. Real usable water and household use can differ.
Geometry and unit conversions are deterministic and use unrounded values internally. Real capacity can differ because tanks may have rounded corners, ribs, domes, tapered walls, wall thickness, non-level installation, or manufacturer-specific nominal sizing. Fill-depth accuracy depends on a level tank and a vertical measurement. Family days and tanker plans are estimates from the usage, reserve, delivery size, and price entered.
Multiply inside length × inside width × inside height after putting all three in the same unit. If dimensions are in metres, multiply cubic metres by 1,000 to get litres. A 1 m × 1 m × 1 m tank is 1,000 litres geometrically.
Choose Vertical cylindrical tank, enter the full inside diameter and inside height, and select their unit. The calculator uses π × radius² × height and converts the result to litres, cubic metres, cubic feet, US gallons, and UK gallons.
The outlet may sit above the bottom, the float valve may stop filling below the top, and rounded corners, ribs, slope, sediment, or cleaning reserve may reduce water that is practically available. Use the manufacturer label when available and adjust the usable percentage.
The calculator uses the area of a circular segment at the entered vertical water depth, then multiplies by tank length. Half the diameter gives half the cylindrical volume, but quarter depth does not give quarter volume.
It depends on usable water and daily household use. Four people using 135 litres each per day use 540 litres daily. With 950 usable litres, the estimate is about 1.76 days. Bathing, washing, gardening, guests, leaks, and appliances can change this materially.
No. One US gallon is 3.785411784 litres, while one UK imperial gallon is 4.54609 litres. Use the gallon standard stated by the tank label, drawing, or supplier.
Yes. Select feet for tank dimensions and inches for fill height or depth. If individual tank dimensions use different units, convert them first with Unit Converter.
No. Enter the quoted size and optional price yourself. Tanker capacities, minimum orders, water sources, delivery charges, access conditions, local rules, and prices vary by city and supplier.
No. It estimates volume and planning quantities only. It does not assess drinking-water quality, contamination, tank hygiene, pipe sizing, pump selection, overflow design, structural support, or plumbing compliance.
This calculator estimates tank volume, usable-water allowance, household storage days, and fill requirements. It does not test water quality, guarantee drinking-water safety, design plumbing or structural support, select a tank or pump, provide municipal rates, or guarantee supplier delivery. For plumbing or structural work, use the tank documentation and consult a qualified plumber or engineer.Read the full disclaimer.