How long does it take to drain a pool?

How long does it take to drain a pool?

Draining time is pool volume divided by the real flow rate of your pump or siphon. A 10,000-litre pool with a 6,000 L/h pump takes under 2 hours. A 50,000-litre pool on the same pump takes about 8 hours. The sections below show how to find your own numbers.

The pool draining formula

Drain time (hours) = pool volume (litres) ÷ real flow rate (litres per hour)

If your pump is rated in litres per minute, multiply by 60 to get litres per hour. If your pool is measured in US gallons, use gallons and gallons per hour instead. The maths is identical.

Step 1: Work out your pool volume

• Rectangular pool: length × width × average depth (all in metres) × 1,000 = litres.
• Round pool: 3.14 × radius × radius × water depth (metres) × 1,000 = litres.
• US gallons: length × width × average depth (all in feet) × 7.48.

Use the average depth for pools with a shallow and deep end, and the actual water level rather than the wall height.

Rated flow vs real flow

Pump ratings are typically measured with no hose length and no height to lift the water. Every metre of hose and every metre of height reduces flow. Many pump manuals include a chart of flow against “head” (lift height) — use the figure that matches your setup.

Measure if you can

Point the discharge hose into a bucket and time it, exactly like the filling bucket test.

Calculate

Enter volume and real flow into the volume & flow calculator. Partial drains only need the volume you’re removing.

Pool drain time chart

Approximate drain times for common pool sizes at different real flow rates:

Pool volume	3,000 L/h	6,000 L/h	12,000 L/h
10,000 L (about 2,640 US gal)	3.3 hours	1.7 hours	50 minutes
25,000 L (about 6,600 US gal)	8.3 hours	4.2 hours	2.1 hours
50,000 L (about 13,200 US gal)	16.7 hours	8.3 hours	4.2 hours
100,000 L (about 26,400 US gal)	33.3 hours	16.7 hours	8.3 hours

Times are volume ÷ flow, rounded. Use your real flow rate, not the rating on the box.

Worked examples

Rectangular pool, full drain

A pool 8 m long, 4 m wide and 1.4 m deep on average holds 8 × 4 × 1.4 = 44.8 m³, or 44,800 litres. At a real flow of 6,000 L/h:

44,800 ÷ 6,000 ≈ 7.5 hours.

Round above-ground pool

A round pool 4.5 m across (radius 2.25 m) with 1.1 m of water holds 3.14 × 2.25 × 2.25 × 1.1 ≈ 17.5 m³, or about 17,500 litres. At a real flow of 4,000 L/h:

17,500 ÷ 4,000 ≈ 4.4 hours.

Partial drain

Lowering the 8 m × 4 m pool above by 20 cm removes 8 × 4 × 0.2 = 6.4 m³, or 6,400 litres. At 6,000 L/h:

6,400 ÷ 6,000 ≈ 1.1 hours.

What changes your real drain time

• Hose length and diameter: long, narrow or kinked hoses cut flow sharply.
• Lift height: pumping water up and over a wall or onto a slope lowers flow.
• Falling water level: submersible pumps work slightly less efficiently as the pool empties.
• Blocked intake: leaves and debris around the pump inlet slow it down.
• Power supply: long extension cords can reduce pump performance.

Submersible pump vs siphon

A submersible pump is usually faster and gives a steadier, measurable flow. A siphon needs no power, but its speed depends on the height difference between the pool surface and the hose outlet, so it is often slow and gets slower as the level falls. For large pools, a pump is usually the practical choice.

The last few centimetres

Most submersible pumps stop pulling water when the level drops to a thin layer, often a centimetre or more. Plan extra time to remove the rest with a wet vacuum, a low-profile pump or a mop, and add that to your estimate.

Practical cautions

Check local rules on where pool water may be discharged, and ask the manufacturer before fully emptying a pool: some pool types can be damaged by groundwater pressure when empty.

Frequently asked questions

How long does it take to drain a pool?

It depends on volume and real flow. A small pool can drain in a couple of hours, while a large in-ground pool on a single pump can take a day or more. Divide the pool's volume in litres by the pump's real flow in litres per hour for your own estimate.

How do I find my pool's volume?

Multiply length, width and average depth for a rectangular pool, or use 3.14 × radius² × depth for a round one. Convert cubic metres to litres by multiplying by 1,000.

Can I drain a pool without a pump?

Yes, with a siphon hose, as long as the outlet end is lower than the water surface. It works without power but is usually slower and depends on the height difference.

Why is my pool draining slower than the pump rating says?

Ratings assume no hose and no lift. Real setups lose flow to hose length, height and friction, so the actual rate is often well below the label. Measure it with the bucket test for an accurate figure.

Is it safe to drain a pool completely?

Not always. Some in-ground pools can be pushed up or damaged by groundwater pressure when empty, and some liners can shrink or crack. Ask the manufacturer or a pool professional before a full drain.

Where can I send the pool water?

Rules vary by area. Many places restrict discharge into storm drains, sewers, streams or neighbouring property, and treated water may need conditions such as chlorine reduction. Check your local council or water authority first.

More pool calculations

Use the volume & flow calculator for your own numbers, or see how long the reverse job takes in the guide to filling a pool.

Last reviewed: October 14, 2026