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Pool volume and tank capacity calculator

Pool volume in gallons, litres and m³ for rectangular, round or oval pools and water tanks, with fill time and the chlorine dose to raise ppm.

Drafted with AI writing toolsUpdated Checked examples: 5

A garden hose gives roughly 20–40 L/min (5–10 gal/min).
ppm
Try
Water volume
L
Water volume: 75,000 L
Maximum decimal places: 1; Nearest, ties away from zero
Water volume
19,812.9US gal / 75m³
Time to fill
1 d 17 h 40 min
Liquid chlorine to add
1.2L / 40.58US fl oz
The average of the two ends assumes the floor slopes evenly; a pool with a hopper or steps holds a little less.

It holds 75,000 L (19,813 US gal) and fills in about 1 d 17 h 40 min at 30 L/min. Raising chlorine by 2 ppm takes 1.2 L of liquid chlorine 12.5%.

Side section (sloping floor)

10 m1 m2 m
How it's calculated S

  1. Volume

    10×5×1+22=75 m310 \times 5 \times \frac{1 + 2}{2} = 75\ \text{m}^3

  2. Litres and gallons

    75 m3=75,000 L=19,812.903927 US gal75\ \text{m}^3 = 75{,}000\ \text{L} = 19{,}812.903927\ \text{US gal}

  3. Fill time

    75,000 L30 L/min=2,500 min\frac{75{,}000\ \text{L}}{30\ \text{L/min}} = 2{,}500\ \text{min}

    1 d 17 h 40 min

  4. Chlorine dose

    2 mg/L×75,000 L=150 g÷125 g/L=1.2 L2\ \text{mg/L} \times 75{,}000\ \text{L} = 150\ \text{g} \div 125\ \text{g/L} = 1.2\ \text{L}

    Liquid strength is the trade percentage: 12.5% means 125 g of available chlorine per litre.

About the pool volume and tank capacity calculator

Volume is the water's surface area times its depth: length × width × average depth for a rectangular pool with a sloping floor, π × radius² × depth for a round pool or upright tank, and π/4 × length × width × depth for an oval. The result is given in litres, US gallons and cubic metres, and the fill time is the volume divided by the flow rate.

The default 10 × 5 m pool, 1 m deep at one end and 2 m at the other, holds 75,000 L (19,813 US gallons) and takes about 42 hours to fill at 30 L/min. Raising its free chlorine by 2 ppm needs 150 g of available chlorine, which is 1.2 L of 12.5% liquid.

One ppm is 1 mg of available chlorine per litre, and the product amount is that mass divided by its strength. Liquid strength is read as trade percent, grams per 100 mL, so 12.5% liquid carries 125 g per litre.

How to calculate pool volume

Multiply the water's surface area by its average depth. A rectangular pool is length × width × average depth; a round pool is π × radius² × depth. Multiply cubic feet by 7.48 for US gallons, or cubic meters by 1,000 for liters. A 10 × 5 m pool sloping from 1 m to 2 m deep holds 75,000 L (19,813 US gallons).

Pool volume formulas by shape

  • Rectangular pool with a sloping floor: length × width × (shallow depth + deep depth) ÷ 2.
  • Round pool or upright cylindrical tank: π × (diameter ÷ 2)² × depth.
  • Oval pool: π ÷ 4 × length × width × depth, or about 0.785 × length × width × depth, using the full length and width.
  • Rectangular tank: length × width × depth.

A cubic foot holds 1,728 ÷ 231 = 7.48 US gallons, and a cubic meter holds 1,000 liters. One US gallon is exactly 3.785411784 L.

Worked examples

Rectangular, metric. The 10 × 5 m pool averages (1 + 2) ÷ 2 = 1.5 m deep, so it holds 10 × 5 × 1.5 = 75 m³, or 75,000 L. Divided by 3.785411784, that is 19,812.9 US gallons.

Round, in feet. A pool 24 ft across with 4 ft of water holds π × 12² × 4 = 1,809.6 ft³. At 7.48 gallons per cubic foot, that is 13,536 US gallons, or 51,241 L.

Oval, in feet. A 30 × 15 ft oval with 4 ft of water holds 0.785 × 30 × 15 × 4 = 1,413.7 ft³, or 10,575 US gallons. The trade shortcut of length × width × depth × 5.9 gives 10,620, because 5.9 rounds up 0.785 × 7.48 = 5.875.

How long does it take to fill a pool?

Divide the volume by the flow rate. The 75,000 L pool takes 2,500 minutes at 30 L/min, about 41 hours 40 minutes. A garden hose typically gives 20 to 40 L/min (5 to 10 gal/min).

To find your own rate, time how long the hose takes to fill a bucket of known size and divide the volume by the minutes. A pump rated in cubic meters per hour converts at 1 m³/h = 16.67 L/min.

Pool and tank examples

Default is the rectangular pool at 30 L/min, and round imperial is the 24 ft pool filled at 9 gal/min. Upright cylinder is a tank 1 m across with 1.2 m of water at 10 L/min.

Oval imperial is the 30 × 15 ft oval at 30 L/min, and rectangular tank is 2 × 1.5 × 1 m at 20 L/min. Fill times are in seconds; divide by 3,600 for hours.

ScenarioLitersUS gallonsFill time, seconds
Default75000.00000019812.903927150000.000000
Round imperial51240.95840213536.42914690242.860973
Upright cylinder942.477796248.9762945654.866776
Oval imperial40031.99875210575.33527080063.997504
Rectangular tank3000.000000792.5161579000.000000

The round pool takes about 25 hours 4 minutes, the oval 22 hours 14 minutes, the cylinder 94 minutes and the tank 2 hours 30 minutes. Topping up needs only the missing volume.

How much chlorine raises a pool by 1 ppm?

One ppm is 1 mg of available chlorine per liter, so grams of available chlorine = ppm increase × liters ÷ 1,000. Use the increase: to go from a measured 1 ppm to 3 ppm, raise by 2 ppm.

Raising the 75,000 L pool by 2 ppm takes 150 g of available chlorine. Divide by the product's strength: 12.5% liquid carries 125 g per liter, so 1.2 L; 65% cal-hypo gives 150 ÷ 0.65 = 230.8 g.

Per 10,000 US gallons, 1 ppm is 37.9 g: about 10.2 fl oz of 12.5% liquid, 12.8 fl oz of 10% liquid or 2.1 oz of 65% cal-hypo, in line with Clean Pool Math.

Liquid strength here is trade percent, grams per 100 mL. Olin's sodium hypochlorite manual explains how that differs from weight percent, and liquid chlorine loses strength in storage.

The dose ignores chlorine demand, the share that contaminants consume. The CDC advises free chlorine of at least 1 ppm in pools and 3 ppm in hot tubs, with pH from 7.0 to 7.8, so test after dosing and follow the label.

Mistakes that throw off the volume

  • Measuring the outside. Use inside dimensions at the water line. A manufacturer's outside size can include the wall thickness and the space above the water.
  • Averaging an uneven floor. The two-depth average assumes an even slope. With a long shallow shelf and a short deep end, measure each section as its own rectangle and add them.
  • Rounding depth loosely. Over the default pool's 50 m² surface, 1 cm of extra average depth adds 0.5 m³, or 500 L.
  • Mixing gallons. An imperial gallon is 4.54609 L, so the 75,000 L pool is 16,498 imperial gallons but 19,813 US gallons.
  • Using a horizontal tank. These formulas assume an upright cylinder; a horizontal one filled partway needs a circular-segment formula.

To compare a supplier's capacity units, use the volume converter; for pump ratings, the flow rate converter.

Worked examples

10 × 5 m pool, 1 m to 2 m deep, +2 ppm with 12.5% liquid

Shape
Rectangular pool
Length
10 m
Width
5 m
Shallow end depth
1 m
Deep end depth
2 m
Fill rate
30 L/min
Raise free chlorine by
2 ppm
Chlorine product
Liquid chlorine 12.5%
Water volume
75,000 L
Water volume
19,812.9 US gal
Time to fill
1 d 17 h 40 min
Liquid chlorine to add
1.2 L
Liquid chlorine to add
40.58 US fl oz

Checked against: 10 × 5 × 1.5 = 75 m³; 75,000 L ÷ 30 L/min = 2,500 min; 2 mg/L × 75,000 L = 150 g ÷ 125 g/L = 1.2 L

24 ft round pool, 4 ft deep, 9 gal/min hose, +1 ppm cal-hypo 65%

Shape
Round pool
Diameter
24 ft
Water depth
4 ft
Fill rate
9 gal/min
Raise free chlorine by
1 ppm
Chlorine product
Cal-hypo 65% (granular)
Water volume
13,536.4 US gal
Time to fill
1 d 1 h 4 min 2 s
Chlorine product to add
78.8 g
Chlorine product to add
2.78 oz

Checked against: π × 12² × 4 ft³ = 13,536 US gal; 51,241 g ÷ 1000 ÷ 0.65 = 78.8 g (Clean Pool Math: 2.1 oz per 10,000 gal·ppm → 2.8 oz)

Upright tank 1 m across, 1.2 m of water, 10 L/min

Shape
Cylindrical tank (upright)
Diameter
1 m
Water depth
1.2 m
Fill rate
10 L/min
Raise free chlorine by
0 ppm
Chlorine product
Liquid chlorine 12.5%
Water volume
942.5 L
Time to fill
1 h 34 min 14 s
Liquid chlorine to add
0 L

Checked against: π × 0.5² × 1.2 = 0.942478 m³; 942.48 L ÷ 10 L/min = 94.25 min

30 × 15 ft oval, 4 ft deep, +3 ppm with 10% liquid

Shape
Oval pool
Length
30 ft
Width
15 ft
Water depth
4 ft
Fill rate
30 L/min
Raise free chlorine by
3 ppm
Chlorine product
Liquid chlorine 10%
Water volume
10,575.3 US gal
Liquid chlorine to add
1.201 L

Checked against: π/4 × 30 × 15 × 4 = 1,413.7 ft³ = 10,575 gal (industry shortcut L × W × D × 5.9 gives 10,620)

Questions

How do you calculate pool volume in gallons?

Multiply length × width × average depth in feet to get cubic feet, then multiply by 7.48, the number of US gallons in a cubic foot (1,728 ÷ 231 cubic inches). A 30 × 15 ft pool averaging 5 ft deep holds 2,250 ft³, or 16,831 gallons. For a round pool use π × radius² × depth: 24 ft across and 4 ft deep holds 13,536 gallons.

How many litres of water are in a pool?

Multiply length × width × average depth in metres, then by 1,000, since a cubic metre holds 1,000 litres. A 10 × 5 m pool sloping from 1 m to 2 m has an average depth of 1.5 m, so it holds 75 m³, or 75,000 L. A round pool 5 m across with 1.2 m of water holds π × 2.5² × 1.2 = 23.6 m³, or 23,562 L.

How do you find the volume of an oval pool?

Multiply length × width × depth by π/4, about 0.785, because an ellipse covers π/4 of the rectangle around it. A 30 × 15 ft oval with 4 ft of water holds 1,413.7 ft³, or 10,575 US gallons. The common shortcut of length × width × depth × 5.9 gives 10,620 gallons, because 5.9 rounds up 0.785 × 7.48 = 5.875.

How much chlorine raises a pool by 1 ppm?

One ppm needs 1 mg of available chlorine per litre, so 10,000 US gallons (37,854 L) needs 37.9 g: about 10.2 fl oz of 12.5% liquid, 12.8 fl oz of 10% liquid or 2.1 oz of 65% cal-hypo. The CDC advises keeping free chlorine at 1 ppm or more in pools and 3 ppm or more in hot tubs, with pH between 7.0 and 7.8.

How long does it take to fill a pool with a hose?

Divide the volume by the flow rate. At 30 L/min the default 75,000 L pool takes 2,500 minutes, about 41 h 40 min, and at 9 US gallons a minute a 13,536-gallon round pool takes about 25 hours. To find your own flow rate, time how long the hose takes to fill a bucket of known size and divide the volume by the minutes.

About this calculator

Vrect=ℓwd1+d22, Vround=πr2d, Voval=π4ℓwd,mCl=ppm×VL mgV_{\text{rect}} = \ell w \tfrac{d_1 + d_2}{2},\ V_{\text{round}} = \pi r^2 d,\ V_{\text{oval}} = \tfrac{\pi}{4}\ell w d,\qquad m_{\text{Cl}} = \text{ppm} \times V_{\text{L}}\ \text{mg}

Sources

  1. Clean Pool Math — chlorine per 10,000 gal per 1 ppm: 13 fl oz of 10% liquid, 2.1 oz of 65% cal-hypo, 2.4 oz of 56% dichlor
  2. PHTA — Sodium hypochlorite (liquid chlorine) fact sheet
  3. CDC — Operating public pools, hot tubs and splash pads (free chlorine and pH levels)

Checked against references

This calculator includes 5 worked examples with independently sourced answers. They run in the test suite, and you can run them here too.

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