Small pool sizes, from 3 to 6 m

How small is a small pool?

The smallest pool worth digging is about 9′ 10″ (3 m) across, a round plunge pool. The largest that still counts as small is about 19′ 8″ (6 m): at 20 × 10 ft (6 × 3 m) a rectangle is a compact pool for a family, and the next size up in the plan library, 23 × 11 ft (7 × 3.5 m), is a family-sized pool. Everything between is a decision about use. Below 6 m nobody swims lengths, so the size fixes what you can do in the water, and the choice is which of those things you want.

This page is about the pool's size. The space around it, with the walkable surround, the gate, the plant room and the noise of the heat pump, belongs to the small garden guide, and it is worth reading both before anything is pegged out. The table gives the real figures for the sizes below, each from its own plan page, and to see which of them fit the garden you have, enter its length and width.

3 m: a round plunge pool

A round pool 9′ 10″ (3 m) across has 75 sq ft (7 m²) of surface and, at the 4′ 3″ (1.3 m) the library draws it, holds about 2,113 gal (8 m³): three or four people standing, nobody swimming. It is a place to cool off on a hot afternoon, to sit on a bench with water to the shoulders, to cool down after a sauna, and it does those things well, with one skimmer, a 10,000 BTU/h (3 kW) heat pump and a fill from a garden tap that takes about five and a half hours.

It is also the size where every metre counts and the shape helps: a circle has no corners for water to stand in, the walls reach the middle from every side, and a cover over it is one piece of round cloth. Digging it takes out about 3,963 gal (15 m³) of soil: a small job for a small excavator.

4 m: the smallest pool two adults can share

At 13 × 8 ft (4 × 2.5 m) a rectangle has 108 sq ft (10 m²) of surface and about 3,170 gal (12 m³) of water at 4′ 3″ (1.3 m), which is the smallest pool two adults share comfortably: chest-deep for most of them, long enough to push off one wall and float, wide enough to pass each other. A bench along one wall seats a third person. It takes about 5,548 gal (21 m³) of excavation and a 17,000 BTU/h (5 kW) heat pump.

A round pool of 13′ 1″ (4 m) has more surface, 135 sq ft (12.5 m²), and holds about 4,227 gal (16 m³) because the library draws it from 3′ 11″ (1.2 m) to 5′ 3″ (1.6 m). It suits a courtyard where nothing rectangular fits, and it is sociable: everybody faces everybody. This is also the size where people ask whether they want a plunge pool or a hot tub, and the comparison answers it.

Below six metres nobody swims lengths, so the size you choose is a decision about what the pool is for.

5 m: where strokes begin

Five metres is the first length at which a few strokes make sense. A 16 × 10 ft (5 × 3 m) rectangle has 161 sq ft (15 m²) of surface and about 5,019 gal (19 m³) of water, and takes a 24,000 BTU/h (7 kW) heat pump. A built-in staircase reaches about 4′ 7″ (1.4 m) into the water, as the steps guide works out, which leaves about 11′ 10″ (3.6 m) of open lane, so corner steps or a ladder are what protect it. Play, floating and a few strokes against a wall: that is what five metres is for.

A 16 × 8 ft (5 × 2.5 m) plan is drawn at one depth of 4′ 3″ (1.3 m) and holds about 3,963 gal (15 m³): a longer plunge pool, not a swimming pool. Round at 16′ 5″ (5 m), the library has 211 sq ft (19.6 m²) of water and about 7,133 gal (27 m³), because it draws it from 3′ 11″ (1.2 m) to 5′ 11″ (1.8 m). Compare sizes at the same depth, or the table misleads you.

6 m: the compact family pool

At 20 × 10 ft (6 × 3 m) a pool has 194 sq ft (18 m²) of surface and about 6,076 gal (23 m³) of water. It fills from a garden tap in about 15 hours, needs one skimmer and a 27,000 BTU/h (8 kW) heat pump, and takes about 10,303 gal (39 m³) of soil out of the ground. It is the smallest pool that a family really uses as a pool: children playing in the shallow end, a parent floating, a short lane for the one who wants a few lengths of exercise.

Entry is the decision at this size. A full-width staircase is most of the shallow end of a 19′ 8″ (6 m) pool, as the steps guide says, so a corner staircase or a ladder keeps the water that matters. A Roman-ended 20 × 10 ft (6 × 3 m) pool holds about 5,283 gal (20 m³) against the rectangle's 6,076 gal (23 m³), and its curved end is where the steps go. Beyond 19′ 8″ (6 m) the pool becomes a pool for the whole family, and the family pool guide takes over.

Shape changes the water more than the length does

In a small pool the shape moves the volume further than a half-metre of length. In the same 20 × 11 ft (6 × 3.5 m) box, a rounded rectangle holds about 6,868 gal (26 m³) of water, a Grecian about 6,604 gal (25 m³), an oval about 5,548 gal (21 m³) and a kidney about 3,963 gal (15 m³), three fifths of the rounded rectangle. The table gives all four.

The kidney is the lesson. Its box says 6 × 3.5 m, and its water says a pool of 5 × 3. Free-form curves look generous in a big garden and cut the swim line in a small one, so choose between an oval or a kidney with the figures in front of you, and keep the outline simple unless the garden can show it off.

Depth: one depth or a slope

The plan pages draw the plunge sizes at a single depth of 4′ 3″ (1.3 m) and the compact sizes sloping from 3′ 11″ (1.2 m) to 5′ 3″ (1.6 m). The small garden guide argues for one depth below about 215 sq ft (20 m²) of water, because a slope this short gives a shallow end too short to play in and a deep end too short to swim in. Both are defensible. What is certain is that depth moves the volume in steps you can compute: 3 7/8″ (10 cm) more across a 20 × 10 ft (6 × 3 m) pool, 194 sq ft (18 m²) of surface, is another 476 gal (1.8 m³).

So decide the depth early and from use. If the pool is mainly for children or cold dips, 3′ 11″ (1.2 m); if adults want to feel submerged, 4′ 7″ (1.4 m); and below 3′ 7″ (1.1 m) the dig is not worth it.

What a small pool costs to run, in water and in machinery

The figures that scale with water scale down with it: fill hours, from about five and a half for the 9′ 10″ (3 m) pool to about 15 for the 20 × 10 ft (6 × 3 m), and the heat pump, from 10,000 BTU/h (3 kW) to 27,000 BTU/h (8 kW). Every plan page prints them, and the table has them. A small volume also swings fast, in temperature and in chemistry, so small doses and frequent testing matter more than in a family pool.

The machinery does not shrink in proportion. A 9′ 10″ (3 m) pool still needs a pump, a filter, a skimmer, pipework and a place for them, and the plant room takes much the same space as for a pool twice the size. What a small pool saves is water, heat and soil, not equipment, which is why the size you pick should come from use and not from a wish to spend less.

Which size for what

Cooling off, sitting in the water and cold dips: 9′ 10″ (3 m) round or 13 × 8 ft (4 × 2.5 m). Two or three people at once, floating and a bench: 13 × 8 ft (4 × 2.5 m) to 16 × 8 ft (5 × 2.5 m). A few strokes, children and company: 16 × 10 ft (5 × 3 m). A family that plays, floats and now and then swims a short lane: 20 × 10 ft (6 × 3 m). If what you want is lengths, none of these will do; that is a lap pool of 32′ 10″ (10 m) or more, and a different guide.

Then peg the outline out in the garden with string for a week. Open the plan page of the size you like in the designer from its button, change the depth and the shape, and read the volume it reports: that is the figure every dose, every fill and every heat pump is sized from. To check an outline that is not on the list, the pool volume calculator measures any of the designer's shapes at your own size.

What goes wrong in practice

1. Comparing boxes, not water

   A kidney, an oval and a rounded rectangle share a 20 × 11 ft (6 × 3.5 m) box and hold 3,963 gal (15 m³), 5,548 gal (21 m³) and 6,868 gal (26 m³). Compare the water, not the box.

2. Expecting to swim lengths

   Under 19′ 8″ (6 m) a staircase and two turns leave a few strokes at best. If swimming is the point, the pool is a lap pool and the size is 32′ 10″ (10 m) or more.

3. A staircase that eats the pool

   A full-width flight reaches about 4′ 7″ (1.4 m) in. In a 16′ 5″ (5 m) pool that is more than a quarter of the length. Move it to a corner or fit a ladder.

4. Choosing the size from the price

   A smaller pool saves water, heat and soil, not the pump, the filter and the plant room. Choose the size for what the pool does, then look at the cost.

5. Ignoring depth when comparing

   A round 16′ 5″ (5 m) pool drawn at 3′ 11″–5′ 11″ (1.2–1.8 m) holds about 7,133 gal (27 m³), a 16 × 10 ft (5 × 3 m) rectangle at 3′ 11″–5′ 3″ (1.2–1.6 m) about 5,019 gal (19 m³). Part of the gap is depth, not size.