Water tank capacity calculator
Find a tank's capacity in litres from its dimensions — rectangular L × B × H or cylindrical π · r² · h — or size a tank from how many people it must serve.
Built around Nepal's water-supply norms, with an LPCD-and-storage-days sizing mode and a suggested set of tank dimensions. A planning-level tool, computed in your browser.
Tank parameters
Inside length of the tank.
Inside width of the tank.
Depth of water — keep below the rim for freeboard.
Tank capacity
3,600 L
3.60 m³ of water
In cubic metres
3.60 m³
Capacity
3,600 L
Volume
3.60 m³
Shape
Rectangular
≈ tankers
0.4
| Volume equation | V = L × B × H |
| Cubic metres | 2 × 1.5 × 1.2 = 3.600 m³ |
| Litres | 3.600 m³ × 1000 = 3,600 L |
A planning-level estimate. Use internal (clear) dimensions and keep the water height below the rim so there is freeboard. Add an overflow, scour and inlet/outlet allowance, and round up to the nearest standard tank size. The suggested dimensions assume a near-cube reinforced tank; real layouts depend on the plot, head and plumbing. LPCD varies by service level — verify the figure for your scheme.
From dimensions to litres
Capacity is just the internal volume of water; sizing works backwards from how much water people use each day and how many days you want to store.
Volume
Rectangular tanks use V = L × B × H; cylindrical tanks use V = π × r² × H. Measure the internal dimensions in metres.
Litres
One cubic metre of water is 1000 litres, so multiply the volume in m³ by 1000 to get the capacity in litres.
Size by demand
Required volume = people × LPCD × storage days. Nepal's design norm is often ≈135 LPCD; add freeboard and round up.
Water tanks, answered
How do I calculate the capacity of a water tank in litres?+
Work out the internal volume in cubic metres, then multiply by 1000. For a rectangular tank, V = length × breadth × water height (all in metres); for a cylindrical tank, V = π × radius² × water height. One cubic metre of water is exactly 1000 litres, so a 2 m × 1.5 m × 1.2 m tank holds 2 × 1.5 × 1.2 × 1000 = 3,600 litres.
What is the formula for a cylindrical tank's capacity?+
Capacity (litres) = π × r² × h × 1000, where r is the inside radius and h is the water height, both in metres. If you only know the diameter, the radius is half of it. For example a tank of radius 0.75 m and water height 1.2 m holds π × 0.75² × 1.2 × 1000 ≈ 2,121 litres.
What is LPCD and what value should I use for Nepal?+
LPCD is litres per capita per day — the water one person uses in a day. Nepal's design norm for piped urban supply is commonly taken as about 135 LPCD, while basic and rural service levels are lower (often 45–100 LPCD). The figure depends on the scheme, climate and service standard, so confirm the value your design authority requires.
How big a tank does a household need?+
Multiply the number of people by the LPCD and by the days of storage you want to hold. For example 6 people × 135 LPCD × 1 day of storage = 810 litres, so a 1,000-litre tank gives a small margin. Add freeboard above the water line and round up to the nearest standard tank size.
Should I use internal or external dimensions?+
Always use the internal (clear) dimensions and the actual water height — not the full tank height. Water never fills a tank to the very top: an overflow, freeboard and the inlet/outlet fittings reduce the usable volume, so measure to the working water level.
How many litres are in one cubic metre?+
Exactly 1,000 litres. So a tank volume of 5 m³ holds 5,000 litres. That single conversion is the heart of every tank-capacity calculation: compute the geometric volume in cubic metres and multiply by 1000.
Sources & data note
Capacity uses the geometric volume (rectangular L×B×H or cylindrical π·r²·h) converted to litres at 1 m³ = 1000 L. Demand sizing uses required volume = persons × LPCD × storage days, with a default of 135 LPCD reflecting a common Nepal piped-supply design norm; rural and basic service levels are lower. LPCD and storage-day requirements vary by scheme and authority — these figures are indicative and you should verify the current design standard before building.