Paving calculator UK: work out slabs, gravel, turf, topsoil and decking quantities and costs

A 20 m² patio costs about £1,600 to £3,800 supplied and installed in London and the South East, depending on the stone and the ground work, and a drain adds more where the patio needs one. This paving calculator works out the quantities and the cost for patios, block paving, turf, topsoil, gravel and decking, in one place rather than five separate tools.

It's written for builders and landscapers pricing a job for a client. Every section works out quantities first (slabs, tonnes of gravel, rolls of turf, decking boards), then the money, and every figure is labelled supplied and installed, supply only or fitting only so nothing gets counted twice.

Paving and landscaping prices at a glance

Every landscaping job has two parts: the ground work (excavation, sub-base, bedding, laying, edge restraints, falls and drainage, final grading) and the material on top. The calculators below work out the quantities first, then the price. Prices are typical current UK prices at London and South East levels, including VAT; elsewhere the same job usually costs less. They are indicative, current as at November 2026, not a quotation.

The low end of each range is the bare minimum: it usually means a thinner sub-base, no drainage, spoil left on site or no allowance for cutting, which is covered in the section on what a low quote leaves out.

Paving slab calculator: how many slabs

A paving calculator for slabs is just area divided by the area of one slab, plus a wastage allowance for cuts. The formula is: slabs = patio area ÷ (slab length × slab width), × the wastage factor, rounded up.

Take a 4 m by 5 m patio, so 20 m². One 600x600 slab covers 0.36 m², which is 2.78 slabs per square metre, so 20 m² needs 56 slabs before cuts and 62 with 10% wastage. A 600x300 slab covers 0.18 m², 5.56 per square metre, so the same patio needs 112 slabs, or 123 with 10%. Most UK slabs are sold by the square metre in patio packs rather than by the slab, so order by area with the wastage already in it.

Wastage and cutting

A square or rectangular patio laid square to the house needs about 5%. Add 10% where there are edges, steps, manholes or a curved border to cut around, and 15% for diagonal, herringbone or circular layouts. Every cut makes an offcut nobody can use, and on a diagonal every slab along two sides is cut twice. Cutting also costs time, which is why a diagonal patio takes longer to lay than a square one of the same area.

Patio cost: sub-base, bedding and laying

The slabs are the cheap part. On a 20 m² patio the stone is often £300 to £1,300, while the excavation, carting the spoil away, 100 mm of compacted hardcore, a full wet mortar bed, the falls and the pointing make up most of the rest. That is where the money goes, and it is the part a cheap quote cuts.

Supply only slab prices, including VAT, sit at roughly £12 to £25 per m² for concrete, £25 to £45 for Indian sandstone and £25 to £60 for porcelain, with limestone and granite above that. The calculator uses mid-range figures of £20, £35 and £40. The cheapest slabs are usually thinner, less consistent in size and colour, and harder to lay level.

A 20 m² patio in Indian sandstone with a new sub-base and no drain comes to about £2,570 at mid-range prices, inside a typical £1,900 to £3,300. In budget concrete slabs it is about £2,240, and in porcelain about £2,680. Add about £360 for a 4 m channel drain along the house, and about £1,000 more if that drain needs a new soakaway. The gap between finishes is almost entirely the stone: the digging, the hardcore and the labour cost the same whichever slab the client picks.

Mortar and bedding quantities

A full wet bed at 40 mm takes roughly 0.04 m³ of mortar per m², which at a 5:1 sharp sand to cement mix is about 70 kg of sharp sand and 14 kg of cement per square metre of slabs, plus pointing on top.

For the 20 m² patio that is about 1.5 tonnes of sharp sand (two bulk bags) and 12 to 14 bags of 25 kg cement including the pointing mortar. Slabs bedded on five dabs instead of a full bed use a fraction of that, which is exactly why the dab method turns up on cheap quotes and why slabs laid that way rock, stain and lift within a few winters. Porcelain and sandstone also need a slurry primer on the back of every slab so the bed bonds to it.

Block paving driveway calculator

A driveway carries vehicle loads, so the ground work is heavier than a patio. A block paved drive costs about £100 to £160 per m² supplied and installed on a Type 1 sub-base, and £130 to £200 per m² on 150 mm of compacted hardcore with a 100 mm concrete base, blocks included. The concrete base is the heavier, dearer build, used where loads are heavy or the ground is poor.

Many drives are laid on a lighter flexible build instead, 150 mm or more of compacted Type 1 and a sand bed with no concrete, and permeable block paving is laid on a clean open graded sub-base so the rain soaks through. Price the sub-base for the build-up the drive actually needs.

Blocks are a supply only item: concrete block paving typically costs £15 to £30 per m² and clay pavers, which hold their colour far better, £35 to £55 per m², including VAT. The calculator uses £22 and £45.

A 40 m² drive in concrete blocks on a concrete base, with a 5 m channel drain at the pavement edge, comes out around £6,600, and around £7,500 in clay pavers. On a Type 1 sub-base the same drive in concrete blocks is around £4,800. Add about £2,500 where the water has nowhere to go and a new soakaway is needed.

Drainage: falls, channel drains and soakaways

Water has to leave a hard surface somewhere, and where it goes decides both the price and whether the job is legal. The figures here are supplied and fitted, including VAT.

Falls. A patio or drive should fall away from the house at least 1 in 80, and 1 in 60 is better, which is 12.5 to 17 mm per metre. A 4 m deep patio therefore drops about 50 to 67 mm from the house to the garden edge. The water runs onto a lawn, a border or a gravel strip, or into a drain along the far edge.

Level against the house. The finished paving should sit at least 150 mm below the damp proof course, so rain cannot splash up above it and soak the wall. Where that is not possible, because the client wants a level threshold to bifold doors or the garden rises towards the house, a channel drain goes along the wall to catch the water.

Channel drains. A domestic channel drain costs about £60 to £120 per metre supplied and fitted, including excavation and the concrete haunching. A drive needs a vehicle rated channel; a pedestrian grade channel under car wheels cracks within a few years. A heavy duty channel with a ductile iron grating runs about £120 to £200 per metre. The drain has to discharge somewhere: an existing rainwater gully or surface water drain, or a soakaway, but never a foul only drain.

Soakaways. A small garden soakaway for a patio costs about £600 to £1,500, and a crate soakaway sized for a drive or a roof about £1,500 to £4,000, supplied and fitted. It needs a percolation test first, because heavy clay may not take the water, and it sits at least 5 m from the house.

Planning for front gardens (England). Where more than five square metres of a front garden is covered with a hard surface that does not drain to a permeable area, planning permission is needed. A permeable or porous surface (gravel, permeable block paving, porous asphalt) needs no permission at any size, and neither does a hard drive whose rainwater runs to a lawn, a border or a soakaway.

A block drive on a concrete base does not drain through, so on a front garden it needs a channel drain to a soakaway or a permeable area, or planning permission. The full rules are in the government's guidance on the permeable surfacing of front gardens. Our page on external works, driveways, patios and fencing goes further into drainage on larger front gardens.

Turf calculator

Rolled turf laid on prepared ground, including the final grading so the lawn sits flat and drains, costs about £15 to £30 per m² supplied and laid in London and the South East, including VAT. Heavy levelling, stripping an old lawn or new topsoil is extra where it is needed.

A standard UK turf roll covers 1 m² (about 610 mm by 1640 mm), and you add about 5% for cutting in around borders and curves. A 50 m² lawn therefore needs 53 rolls, and costs about £1,100 at a mid-range £22 per m².

Topsoil calculator

After a new build, an extension or any job where plant has crossed the garden, the ground is compacted and full of rubble just under the surface, so new topsoil is usually the safer assumption. A lawn needs 100 mm of good topsoil; a planted border wants 150 mm or more.

Quantity is area × depth. At 100 mm, 1 m² needs 0.1 m³. Screened topsoil weighs about 1.3 tonnes per m³ as delivered, so a 50 m² lawn at 100 mm needs 5 m³, about 6.5 tonnes, which is eight bulk bags of about 850 kg. Screened topsoil costs about £55 to £110 a bulk bag supply only, including VAT, and the calculator uses £75. Supplied, spread and levelled at 100 mm, it runs about £15 to £30 per m².

A 50 m² lawn with new topsoil and turf together comes to around £2,200 supplied and fitted, within a typical £1,500 to £3,000.

Gravel calculator

Gravel is bought by weight, so the quantity depends on area and depth. Allow 50 mm for a path or border and 50 to 75 mm for a drive over a proper sub-base, otherwise the gravel migrates and you see the hardcore. Loose 20 mm gravel weighs about 1.6 tonnes per m³, so one tonne covers roughly 12 m² at 50 mm.

Gravel is sold per bulk bag of about 800 kg, supply only: standard 20 mm gravel and shingle around £75 a bag, decorative gravel such as slate chippings or Cotswold stone £100 to £180 a bag, including VAT and before delivery. The calculator uses £75 and £120. A finished gravel path or drive, dug out, with membrane, edging and a sub-base, costs about £40 to £75 per m² supplied and fitted.

A 15 m² gravel path at 50 mm needs 1.2 tonnes, two bulk bags, at about £150 in standard gravel or £240 in decorative. The ground work under it (dig out, membrane, edging) is the real cost: the finished path is about £825 at a mid-range £55 per m², and on a drive it needs the same sub-base a block drive needs.

Decking calculator

A ground level deck (subframe, joists, boards and fixing) costs about £80 to £140 per m² in treated softwood and £130 to £220 per m² in composite, supplied and installed in London and the South East.

For quantities, a common UK board is 145 mm wide by 3.6 m long. With a 5 mm gap each board covers about 0.54 m², so you need 1.85 boards per m², plus 10% for cuts. Joists at 400 mm centres work out at about 2.5 linear metres of 47x100 timber per m² of deck, plus noggins. A 15 m² deck therefore takes about 31 boards and around 42 linear metres of joist.

Boards on their own, supply only, are typically £20 to £35 per m² in pressure treated softwood and £45 to £90 per m² in composite, including VAT. The calculator uses £28 and £80, with 10% for cuts.

A 15 m² deck in treated softwood comes out around £1,590, and in composite around £2,450. Raised decks on posts, steps and balustrade are extra and priced separately.

Garden steps and changes in level

Where the patio or drive sits at a different level to the garden, steps are a separate item from the per square metre paving rate. A solid concrete garden step costs about £150 to £350 each, supplied and fitted, covering the formwork, concrete and finish ready for the client's choice of paving or render.

Retaining edges, sleeper walls and a sloping garden are also separate. A garden that falls more than about 300 mm across the patio area usually means either a retaining wall or extra muck away, and neither is in a per square metre paving price.

What a low paving quote leaves out

A quote at half the price is not the same job at a discount. In paving, the gap is almost always in the same places:

• No excavation depth: the slabs go on 50 mm of whatever is there rather than 100 mm of compacted hardcore.
• Slabs bedded on dabs or spots of mortar instead of a full wet bed, so they rock and stain.
• No falls and no drainage, so water sits against the house wall, or the paving finishes less than 150 mm below the damp proof course.
• A pedestrian grade channel drain across a drive, which cracks under the car.
• Spoil left on site in a pile behind the shed instead of carted away.
• No cutting allowance, so the awkward edges are filled with offcuts and mortar.
• No primer or slurry on the back of porcelain or sandstone, which is why slabs lift.

None of that shows on the quote, and all of it shows two winters later. If you give a client a low figure and a high one, say in one line what the difference buys, or the lowest number wins and the argument comes later.

Worked example: a 4 m by 5 m patio, start to finish

A 20 m² Indian sandstone patio against the back of the house, with a level threshold to the kitchen doors, so it needs a channel drain along the wall into the existing rainwater gully. Typical mid-range prices at London and South East levels, including VAT.

That assumes side access, spoil removed from site, no steps and no retaining wall. A patio priced as its own job carries its own preliminaries in construction: a skip, protection to the hallway and parking for one visit, typically 10 to 15% of the total and already inside the figures above, not added on top.

Where the drain has nowhere to go, add about £1,000 for a small soakaway. Add steps at about £150 to £350 each, and price any retaining work separately. For the concrete and hardcore volumes behind the ground work, our concrete and sub-base calculators do the cubic metres and the ready mix quantity, and our house material estimator works out quantities for the rest of a build, such as bricks, timber and plasterboard.

Paving calculator FAQ

How many paving slabs are in a square metre?

There are 2.78 slabs per m² at 600x600, 5.56 at 600x300, 4.94 at 450x450 and 1.85 at 900x600. Multiply by your area and add 5 to 15% for cuts depending on the layout.

How deep should a patio sub-base be?

For a domestic patio on reasonable ground, 100 mm of compacted hardcore under a 40 mm mortar bed, so about 150 to 170 mm of dig below the finished paving level depending on the slab. A drive needs 150 mm of hardcore or more, and a concrete base where loads are heavy or the ground is poor.

Which way should a patio fall?

Away from the house, at least 1 in 80 and better 1 in 60, with the finished paving at least 150 mm below the damp proof course. Where it cannot fall away or sit that low, a channel drain along the wall takes the water to a gully or a soakaway.

How many tonnes of gravel cover a square metre?

At 50 mm deep, about 0.08 tonnes per m², so one tonne covers roughly 12 m². At 75 mm it is 0.12 tonnes per m², around 8 m² per tonne.

How much does a patio cost per m² supplied and fitted?

In London and the South East, about £80 to £190 per m² including VAT, depending on the slab: concrete at the lower end, sandstone and porcelain higher. That includes the dig out, 100 mm sub-base, full mortar bed and pointing. Drainage is extra where it is needed.

Do I need planning permission to pave a front garden?

In England, only if more than five square metres is covered with a hard surface that does not drain to a permeable area. Permeable paving, gravel, or a drive that drains to a lawn, a border or a soakaway avoids it.

Pricing the whole job

These calculators give a realistic budget for each element, but most garden jobs combine several: a patio with steps and a drain, a drive with a new border, turf and topsoil around the edge of an extension. Our building work estimator puts those elements together into one priced job, and where you need the cost of the whole build rather than just the landscaping, our construction cost calculator covers that wider ground.

Where a client wants a document they can hold you to, Builder Expert's detailed estimating service prices the whole job from your drawings, trade by trade, and our construction estimating software lets you build the same priced paving calculator style estimate yourself in minutes for the next patio, drive or deck you quote.