Pool sizes and depths: how to choose the right size

Leave a walkway of at least 1.20 metres on every side; if sun loungers will line one side, that side goes up to 2.50 metres. Projects that cut this margin leave no room to walk in the garden once they are finished.

The distance to the plot boundary depends on local zoning regulations, and it is the one point that must be confirmed with the municipality. A pool design pushed up against the neighbour's wall gets sent back at the permit stage; you need to find this out before digging starts.

The plant room needs its own space from the start: 4 to 6 square metres with a clear height of no less than 1.80 metres. Put it far from the pool and pipe friction losses rise, the pump moves up a power size, and the electricity bill pays for it every month. Ideally it stays within 8 metres of the pool edge.

Adults can stand, children can get in with help, and it is deep enough for swimming. A constant depth also makes the water volume predictable, which is what heating and chemical calculations are based on.

For clients who want varying depth, our usual layout is a floor that slopes from 1.20 metres down to 1.80 metres. The slope should not exceed 6 percent; on steeper floors feet slip and the floor finish wears out early. Having the shallow section cover at least half the pool length is a matter of comfort: the deep section gets used less than people expect at the start.

If there is a separate children's area, 30 to 40 cm is enough, and it should be physically separated from the main pool. A children's section added as a step inside the main pool means a child is one step away from deep water. In public pools this separation is mandatory; residential pools are not bound by that rule, but it should be followed all the same.

A 1-metre springboard needs a depth of more than 3.40 metres in front of the board and a specific safety geometry for the pool. Reaching that depth means more excavation, a heavier reinforced concrete section and more water; heating costs rise accordingly.

Building the pool 2 metres deep and adding a diving board is a common and dangerous mistake. This is exactly where head and neck injuries happen. If people want to dive, the right answer is a separate diving pool or a non-slip platform at the pool edge for racing starts.

For swim training, what helps is length and a counter-current unit, not depth. Fitting a counter-current unit to a 12-metre pool is both cheaper and more useful than going down to 3 metres deep.

A 4x8 pool is enough for two to four people and is economical to heat and maintain. A 5x10 pool gives families who host guests and spend time by the water a real swimming area.

In a villa garden, position the pool in relation to the house rather than the view. A direct line of sight from the living room to the pool visibly increases how often it gets used. A pool you cannot see from the house stays closed in most homes once the excitement of the first summer wears off.

On sloping plots, overflow systems and infinity edges come up. This choice does not directly change the pool size, but it needs extra space in the plant room for the balance tank and it thickens the reinforced concrete section. Make the decision after the soil survey.

We also build 2.50x5 metre plunge pools; you cannot swim in them, but you can get in the water all summer and they do not swallow the whole garden. The biggest advantage of a small pool is its low water volume: it heats quickly, uses few chemicals and takes little time to maintain.

In narrow gardens, place the pool along one side on its long axis, not in a corner. A pool set in a corner leaves unusable triangular leftovers on two sides. Placing it along the long side leaves a single, usable terrace area.

For homeowners who need to swim but lack the space, we suggest a swim spa with counter-current. It lets you swim in place in a 4-metre body and can be used in winter too. For someone expecting a classic pool it is not satisfying, and we say so from the start.

A 5x10 metre pool with an average depth of 1.50 metres holds 75 cubic metres of water. For residential pools the target is for the full water volume to pass through the filter in 6 hours, which means a pump with a flow rate of 12 to 13 cubic metres per hour.

The same calculation gives the filter diameter. For a flow of 12 cubic metres per hour, a Ø600 mm tank is the typical choice for a sand filter. An undersized filter leaves the water cloudy; an oversized one wastes water during backwashing. Pipe diameter follows from this too: at this flow, Ø50 mm is borderline, while Ø63 mm runs comfortably.

For heating, what counts is surface area, not volume, because most heat is lost through evaporation from the water surface. A 50 square metre surface needs a noticeably more powerful heat pump than a 32 square metre one. A pool cover brings this cost down considerably, and the larger the pool, the faster the cover pays for itself.

Construction costs are low, the plant room is small, and it adds no constraint to the choice of size. Surface cleaning depends on the wind and the number of skimmers; in a 5x10 pool, two skimmers do twice the work of one.

In an overflow pool the water is level with the edge and flows into a grating on all four sides. It looks noticeably better and the surface cleans itself. In return it needs a balance tank: allow roughly 60 to 80 litres of volume for every square metre of pool surface. For a 50 square metre pool that means a separate tank of 3 to 4 cubic metres, and the plant room grows accordingly.

Do not settle the size before choosing the system. If the pool will be an overflow type, the edge level, overflow channel width and grating size add 40 to 50 cm to the outer dimensions. On projects that are already tight in the garden, this difference can be large enough to affect the permit.

An Olympic pool is 50 metres long, and the short-course pool often called semi-Olympic is 25 metres. The width is 25 metres, there are 8 or 10 lanes, and each lane is 2.50 metres wide. For international competition the depth does not go below 2 metres, and 3 metres is preferred in new facilities.

Tolerances on these dimensions are down to the millimetre, because the thickness of the touch pads for electronic timing counts towards the pool length. Once the pads are fitted, the inside length has to be exactly 50 metres, so the structural shell is cast a few centimetres longer than 50 metres.

Hotel, residential complex and school projects often do not need a full Olympic size. A 25-metre pool is more than enough for training and competition, and operating costs drop to a quarter. We cover homologation, spectator stands and climate control for Olympic pool construction in a separate article.

As the pool grows, water volume, heating load, chemical use and cleaning time all grow with it. The first summer is fun; from the second summer on, the big pool starts to stay closed.

The second mistake is deciding on the size separately from the equipment and the plant room. In projects where a spot for the plant room is sought only after excavation is finished, the solution is always a poor one: the pump ends up far away, the pipes get longer and the noise gets closer to the house.

Before you decide on a size, ask for these three numbers: water volume in cubic metres, hourly turnover flow rate, and the clear floor area needed for the plant room. With these three in hand, you can compare quotes and avoid surprises once the pool is finished.