FREE TOOL · WORKS FOR OVERHEAD TANKS AND SUMPS
Water tank size calculator: how many litres does your tank hold?
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Enter your tank's measurements to see how many litres it holds and its cleaning price.
365-plan members get ₹149 off each extra tank cleaned in the same visit. One-time bookings are priced tank by tank.
How to measure your tank
- Check for a printed capacity first. Plastic overhead tanks usually have it moulded or printed on the side or lid. If you can read it, you don't need to measure.
- Pick the shape. Box-shaped (most concrete tanks and sumps), round and standing upright (most plastic roof tanks), or round and lying on its side (some loft and loader tanks).
- Measure the inside if you can. For a box, measure length and width through the opening and drop a weighted tape to the floor for depth. For a round tank, measure straight across the top for the diameter, or wrap a tape around it and divide by 3.14.
- Note the water depth (optional). Push a stick or weighted tape down to the floor and see where it's wet; that tells you how much water is in the tank right now.
Never climb into a sump to measure it. A sump is a confined space; measure through the opening, or send us a photo with a tape against the opening.
The formulas the calculator uses
| Tank shape | Volume formula | What you measure |
|---|---|---|
| Box (rectangular) | V = length × width × depth | Inside length, width, depth |
| Round, upright | V = π × r² × height (r = diameter ÷ 2) | Diameter, height |
| Round, on its side, full | V = π × r² × length | Diameter, length |
| Round, on its side, part-filled to depth h | V = length × (r² × cos⁻¹((r − h) ÷ r) − (r − h) × √(2rh − h²)) | Diameter, length, water depth |
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| Your units | To get litres, multiply the volume by |
|---|---|
| Cubic feet | 28.3168 |
| Cubic metres | 1,000 |
| Cubic inches | 0.016387 |
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1 cubic foot = 28.3168 litres; 1 cubic metre = 1,000 litres; 1 US gallon = 3.7854 litres. For a box or upright tank, swap the depth or height for the water depth to see how much water is in it now.
Sources: litre conversions from the exact definitions 1 ft = 0.3048 m and 1 in = 2.54 cm (NIST SI conversion tables, Special Publication 811); circle-segment area formula from standard geometry. Every row checked in Python on 9 Oct 2026.
Worked examples
| Tank | Measurements | Working | Capacity | Price band (incl. GST) |
|---|---|---|---|---|
| Concrete roof tank, box | 5 × 4 × 4 ft inside | 80 cu ft × 28.3168 | about 2,270 L | Overhead 2,001–5,000 L: ₹1,499 |
| Concrete sump, box | 8 × 6 × 5 ft inside | 240 cu ft × 28.3168 | about 6,800 L | Sump 5,001–10,000 L: ₹2,799 |
| Concrete sump, box (metres) | 2.5 × 2 × 1.8 m inside | 9 m³ × 1,000 | 9,000 L | Sump 5,001–10,000 L: ₹2,799 |
| Same sump, today's water | water 1.2 m deep | 2.5 × 2 × 1.2 = 6 m³ | 6,000 L in it now | Price stays ₹2,799 (priced by full size) |
| Round plastic roof tank, measured outside | 1.10 m across, 1.10 m tall | π × 0.55² × 1.10 m³ | about 1,050 L | Near a band edge: check the printed label |
| Same tank, measured inside | 1.06 m across, 1.06 m deep | π × 0.53² × 1.06 m³ | about 940 L | Overhead up to 1,000 L: ₹699 |
| Round tank lying on its side | 48 in across, 72 in long | π × 24² × 72 cu in × 0.016387 | about 2,140 L | Overhead 2,001–5,000 L: ₹1,499 |
| Same tank, 12 in of water | water 12 in deep | Part-filled formula | about 420 L in it now | Price stays ₹1,499 |
| A large sump | 20 × 15 × 6 ft inside | 1,800 cu ft × 28.3168 | about 50,970 L | Above 30,000 L: quote after a free visit |
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Capacities rounded to the nearest 10 litres. Two tanks in one visit, a roof tank of up to 1,000 L and the 6,800 L sump: ₹699 + ₹2,799 = ₹3,498. For a 365-plan member, ₹149 comes off the second tank: ₹3,498 − ₹149 = ₹3,349.
Sources: AHC price book, 6 Oct 2026 (tank bands); owner's answer Q27, 9 Oct 2026 (365-plan members get ₹149 off each extra tank in the same visit; no multi-tank discount on one-time bookings); each calculation run in Python, 9 Oct 2026.
Inside or outside measurements?
Capacity is the space inside the tank, so inside measurements give the right answer. Outside measurements include the walls and the lid, so they always read high. On a plastic roof tank the gap is small but can push a 1,000-litre tank into the next band, as the example above shows; on a concrete tank with thick walls it can be large.
- Can't get inside? Measure the outside, then take off twice the wall thickness from each length, width and diameter, and the lid and floor thickness from the height.
- Plastic tank? Trust the printed capacity over a tape measure.
- Tank never fills to the top? The overflow pipe sets how high water can rise. For the water a tank really holds, measure the height to the overflow pipe instead of to the lid.
Common tank sizes
Plastic overhead tanks are usually sold as 500, 750, 1,000, 1,500 and 2,000 litres, and many homes have two on the roof. Concrete sumps under parking or a courtyard are built to the plot, from a few thousand litres in a builder floor to tens of thousands in a society. For an upright round tank about as tall as it is wide, these are the sizes the formula gives:
| Capacity | Diameter and height, if equal |
|---|---|
| 500 L | about 0.86 m (2 ft 10 in) |
| 1,000 L | about 1.08 m (3 ft 7 in) |
| 1,500 L | about 1.24 m (4 ft 1 in) |
| 2,000 L | about 1.37 m (4 ft 6 in) |
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Real tanks vary by make and shape, so measure yours or read its label; this table only shows what each size looks like.
Sources: sizes 500–2,000 L from AHC's overhead tank page (common printed capacities); diameters from the upright-cylinder formula, d = ∛(4V ÷ π), run in Python on 9 Oct 2026.
Your tank size and its cleaning price
| Tank | Capacity | Price (incl. GST) |
|---|---|---|
| Overhead | Up to 1,000 L | ₹699 |
| Overhead | 1,001-2,000 L | ₹999 |
| Overhead | 2,001-5,000 L | ₹1,499 |
| Underground sump | Up to 1,500 L | ₹1,199 |
| Underground sump | 1,501-3,000 L | ₹1,499 |
| Underground sump | 3,001-5,000 L | ₹1,999 |
| Underground sump | 5,001-10,000 L | ₹2,799 |
| Underground sump | 10,001-15,000 L | ₹3,299 |
| Underground sump | 15,001-20,000 L | ₹3,799 |
| Underground sump | 20,001-30,000 L | ₹4,499 |
| Above 30,000 L | Society / commercial | Free visit, then fixed quote |
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365-plan members get ₹149 off each extra tank cleaned on the same visit.
Tank cleaning is priced by the type of tank and its full capacity, not by how much water is in it on the day.
| Overhead tank | Price incl. GST | Underground sump | Price incl. GST |
|---|---|---|---|
| above 30,000 L | Quote after a free visit |
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365-plan members get ₹149 off each extra tank cleaned in the same visit. What the clean includes, and how often to book →
Source: AHC price book, 6 Oct 2026 (overhead above 5,000 L by quote, as on the tank hub and the overhead tank page).
Tank size questions
How do I calculate how many litres my tank holds?
How many litres is a 5 × 4 × 4 ft tank?
How many litres are in one cubic foot?
What size is a 1,000-litre tank?
My calculation and the printed capacity don't match. Which is right?
Is the cleaning price based on how much water is in the tank?
I can't measure my sump. What now?
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