How do I calculate concrete for a pool deck?

Work out the outer footprint including the deck, then subtract the pool. For a rectangular pool that is (length + twice the deck width) times (width + twice the deck width), less the pool area. The result multiplied by the slab thickness is your concrete. The shortcut formula is 2w(L + W) + 4w², where w is the deck width — the second term is the four corners, and forgetting it under-orders by a surprising amount on a wide deck.

How wide should a pool deck be?

At least 900 mm anywhere you need to walk, and 1.2 metres is the width at which walking round the pool stops feeling tight. If you want loungers along one side you need about 1.8 metres, and 2.4 gives you furniture with room to walk behind it. Bear in mind that deck area grows faster than width because of the corner term, so going from 1.2 to 2.4 metres on a 10 by 5 pool takes the deck from 41 to 96 square metres — more than double the concrete for double the width.

Why do pool decks crack at the corners?

Because a rectangular pool creates four re-entrant corners in the slab, and a re-entrant corner is a stress concentration. As the concrete shrinks during curing, and later as it moves with temperature, the stress finds the sharpest point of geometry it can and relieves itself there. A diagonal control joint radiating outward from each pool corner gives that stress a defined place to go, so the crack forms straight, in the joint, and stays tight. It goes in regardless of what the spacing rule says, because the corner will crack whether or not a joint happens to fall nearby.

How thick should a pool deck be?

A hundred millimetres is adequate for a pedestrian deck on a well-compacted sub-base, and 125 gives a useful margin, particularly around the shallow end where people congregate. Go to 150 where a vehicle might ever cross — a service route for pool equipment, or a deck that doubles as a turning area. The extra thickness also buys you slightly wider joint spacing, though on a narrow deck the panel-shape rule usually governs and the thickness makes no difference to it.

Which way should a pool deck slope?

Away from the water on every side, at about one in fifty — roughly 20 mm of fall per metre of deck width. Water running back into the pool carries dirt, leaves, grass clippings and sun cream straight into the filtration system, which is both a maintenance cost and a water chemistry problem. A deck that ponds is worse still, because standing water on a smooth surface where people walk barefoot is exactly the accident you spent money to avoid. Slope it out to a drain, a channel, or simply to the surrounding ground.

What surface finish should a pool deck have?

Something with texture, and never a smooth steel-trowelled finish. Wet concrete underfoot with bare feet is the highest-slip-risk surface in a domestic garden, and a polished deck is dangerous the moment anyone climbs out. A broom finish is the simplest answer and works well. Exposed aggregate, textured stamping and salt finishes all give grip too and look better, at more cost. Whatever the texture, keep it fine enough not to graze knees and feet, which rules out the coarsest brooming.

Should the deck be tied to the pool shell?

No. The deck and the pool structure should be free to move independently, with an expansion joint between them filled with a flexible sealant. They sit on different things and respond differently to temperature and ground movement, and rigidly connecting them means whichever is weaker cracks. The joint also needs maintaining: the sealant degrades in sunlight and chlorine and should be inspected annually, because once water gets behind the coping it undermines the deck from below.

Do I need reinforcement in a pool deck?

It is worth it here more than on a typical path. The ground around a new pool is almost always disturbed — it has been excavated and backfilled — and backfill settles for years afterwards. Steel or fibre will not stop the deck cracking if the ground beneath it moves, but it holds the pieces together and keeps a crack tight rather than letting it open into a trip hazard next to the water. Mesh through the slab, well supported on chairs, is the usual approach.

How much waste should I allow on a deck pour?

Ten percent as a minimum, and a deck justifies it more than a plain slab does. A ring is nearly all edge, there is a great deal of cutting and trimming around the coping, and access is awkward because everything has to be barrowed around a hole in the ground rather than straight across it. Running short is also worse here than usual, since the joint where you restart will be visible on a surface people look at closely and walk on barefoot.

Pool Deck Concrete Calculator

A pool deck is the one concrete job where the most expensive mistake is arithmetic rather than technique. The deck is a ring — a band of concrete around a hole in the ground — and the temptation is to measure the outer rectangle, multiply by the thickness, and order that. For a ten by five metre poo...

THE DECK

POOL LENGTH (m)

POOL WIDTH (m)

DECK WIDTH ALL ROUND (m)

1.5 m is comfortable for walking around the pool, though it leaves little room for furniture.

SLAB THICKNESS (mm)

SUB-BASE (mm)

EXTRA DECK AREA (m²) — SUN DECK, STEPS, PLANT AREA

The ring above assumes an even width all round. Anything beyond that — a wider sun deck at one end, a landing at the steps — goes here as a plain area.

CONCRETE REQUIRED

7.43 m³

54.00 m² of deck at 125 mm · including 10% waste · 17.82 tonnes

SUB-BASE

11.34 t

EDGING

72.0 m

JOINTS

The pool is a hole, not part of the pour. The outer footprint is 104.00 m², but 50.00 m² of that is water. You are pouring the 54.00 m² band around it — 52% of the footprint. Ordering for the whole rectangle is the classic way to end up with several cubic metres of concrete going off on the driveway.

Outer footprint

104.00 m²

Pool (not poured)

50.00 m²

Deck ring

54.00 m²

Extra area

None

Concrete before waste

6.750 m³

With 10% waste

7.425 m³

Weight

17.82 t

Sub-base to order

6.750 m³ loose

Inner + outer edging

30.0 + 42.0 m

Bags / loads

438 / 1

LAYING IT

Excavate the ring to 225 mm below finished level and form both edges — 72.0 m in total, inner and outer.

Lay and compact 6.750 m³ of sub-base to a finished 100 mm, keeping it clear of the pool shell.

Place 7.425 m³ of concrete, screeding to a fall of about 1 in 50 away from the water on every side.

Cut 16 control joints, including a diagonal at each pool corner. Corners are where a deck cracks first, so they get a joint whether the spacing calls for one or not.

THE DECK

16 joints at 2.25 m centres. Panel shape governs the spacing rather than slab thickness, as it usually does on a band this narrow. The four diagonals at the pool corners are not optional: a re-entrant corner concentrates stress, and a deck without them cracks diagonally outward from each one within a couple of seasons.

The fall matters more here than on any other slab. Water running back into the pool carries dirt, leaves and whatever was on the deck into the filtration, and a deck that ponds is slippery in exactly the place people walk barefoot.

Live calculation · updates as you type

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HOW TO USE

1
Choose the pool shape and enter its dimensions. For a rectangle that is the water surface length and width; for a round pool, the diameter. These are the pool itself, not the excavation.
2
Set the deck width you want all the way round. The note underneath tells you what that width actually allows — under 900 mm two people cannot pass, and loungers need about 1.8 metres.
3
Set the slab thickness and sub-base depth. A deck is a pedestrian surface, so 100 to 125 mm covers it, on 100 mm of compacted sub-base.
4
Add any area beyond the even band — a wider sun deck at one end, a landing at the steps — in the extra area field, since the ring formula assumes a uniform width.

THE FORMULAS

Rectangular deck2w(L + W) + 4w²

Round deckπ × w × (D + w)

Outer footprint(L + 2w) × (W + 2w)

Concretedeck area × thickness × (1 + waste)

Sub-base to orderarea × depth × 1.25

Edginginner perimeter + outer perimeter

Joint spacingmin(24 × thickness, 1.5 × deck width)

Joints (rect)4 corners + runs at spacing

DECK WIDTH — WHAT IT BUYS YOU

Width	In feet	What it allows	Deck for a 10 × 5 m pool
0.9 m	3.0 ft	Tight walkway, no furniture	30.2 m²
1.2 m	3.9 ft	Comfortable to walk around	41.8 m²
1.8 m	5.9 ft	Room for loungers along one side	67.0 m²
2.4 m	7.9 ft	Furniture with circulation behind	95.0 m²

Deck area grows faster than the width because of the corners — the 4w² term. Going from 1.2 m to 2.4 m does not double the concrete, it more than doubles it. Worth knowing before deciding the width on cost grounds alone.

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Last updated: July 28, 2026 · Formula verified · Eagle-eyed accuracy for every calculation.