Patio and paving calculator
Count slabs or pavers including joint widths, then size the sub-base, bedding mortar, jointing compound and edge restraints for the whole build-up.
Your project
Quick start
Patio area
Add a section for each part of the patio and subtract anything not being paved.
Paving slabs
All units the same size.
2,200 kg/m³
10 mm is typical for slabs; 2–5 mm for block paving.
Joints line up in both directions. The least wasteful pattern to cut.
The calculator warns you if this is below the recommended figure for your pattern.
Build-up and jointing
100 mm for a pedestrian patio, 150 mm or more over soft ground or for vehicles.
Standard for slabs. Estimated as sand and cement.
Block paving and sand-bedded paving must be restrained at every free edge.
Estimate updated. 60 paving slabs of 600 mm × 600 mm paving slabs required.
Patio and paving calculator
United Kingdom · Metric units · 30 July 2026
Shopping list
5 lines- 60paving slabs600 mm × 600 mm paving slabsConcrete paving, 35 mm thick — about 27.7 kg each
- 7bulk bagsMOT Type 1 sub-base100 mm compacted
- 2bulk bagsSharp sandFor a 40 mm mortar bed
- 1225 kg bagsCement1:5 cement to sharp sand bedding mortar
- 320 kg tubsBrush-in jointing compoundSold in tubs by weight. Fill joints to full slab depth for a durable joint.
Estimate results
What you measured
- Patio area
- 20.00 m²
- 215.28 ft²
- Laying pattern
- Straight grid (stack bond)
- Paving weight
- 1.66 tonnes (3,667 lb)
- approx. 2 pallets
What to buy
10% waste included| Material | Buy | Weight |
|---|---|---|
600 mm × 600 mm paving slabs Concrete paving, 35 mm thick — about 27.7 kg each Rounding: The calculation requires 53.75 paving slabs. Adding 10% waste gives 59.12. Rounded up to 60 paving slabs. Main material | 60paving slabs | 1,663 kg |
MOT Type 1 sub-base 100 mm compacted Rounding: The calculation requires 6.12 bulk bags. Adding 10% waste gives 6.73. Rounded up to 7 bulk bags. Base and membrane | 7bulk bags | 5,950 kg |
Sharp sand For a 40 mm mortar bed Rounding: The calculation requires 1.51 bulk bags. Adding 10% waste gives 1.66. Rounded up to 2 bulk bags. Bedding and mortar | 2bulk bags | 1,700 kg |
Cement 1:5 cement to sharp sand bedding mortar Rounding: The calculation requires 10.24 25 kg bags. Adding 10% waste gives 11.26. Rounded up to 12 25 kg bags. Bedding and mortar | 1225 kg bags | 300 kg |
Brush-in jointing compound Sold in tubs by weight. Fill joints to full slab depth for a durable joint. Rounding: The calculation requires 1.82 20 kg tubs. Adding 10% waste gives 2. Rounded up to 3 20 kg tubs. Consumables | 320 kg tubs | 60 kg |
Assumptions behind each line
600 mm × 600 mm paving slabs
- Each paving slab occupies a 610 mm × 610 mm module once the joint is included.
- Straight grid (stack bond): Joints line up in both directions. The least wasteful pattern to cut.
- Concrete paving taken as 2,200 kg/m³.
MOT Type 1 sub-base
- Includes a 1.3× compaction allowance.
- Lay and compact in layers no thicker than 100 mm (4 in).
Sharp sand
- Based on 1.6 tonnes of sand per cubic metre of 1:5 mortar, which allows for bulking.
Cement
- 320 kg of cement per cubic metre of 1:5 mortar, supplied in 25 kg bags.
- Mix only what you can lay before it goes off.
Brush-in jointing compound
- Joint volume is 3.3% of the surface area (0.02 m³ (0.03 yd³)), filled to the full slab depth.
- Jointing material taken as 1,600 kg/m³. Check the manufacturer's coverage table for your specific product.
Laying layout
How this was calculated
Patio area
plus Main area (5 × 4 m) = 20.00 m²
= 20.00 m² (215.28 ft²)
Module size including joint
(600 mm + 10 mm) × (600 mm + 10 mm)
= 0.3721 m² per paving slab
- That is 2.69 paving slabs per m² (0.25 per ft²).
paving slabs required
The calculation requires 53.75 paving slabs. Adding 10% waste gives 59.12. Rounded up to 60 paving slabs.
= 60 paving slabs
Sub-base volume
20.00 m² (215.28 ft²) × 100 mm × 1.3 compaction
= 2.60 m³ (3.40 yd³)
Mortar bedding
20.00 m² (215.28 ft²) × 40 mm = 0.80 m³ (1.05 yd³) of mortar
= 1.28 t sand + 256 kg cement
- Mix ratio 1:5 cement to sharp sand.
Jointing volume
(1 − 0.9675) × 20.00 m² (215.28 ft²) × 35 mm joint depth
= 0.02 m³ (0.03 yd³)
- Joints occupy 3.3% of the paved surface at a 10 mm joint width.
Weight and delivery
Approximate weight
9.67 tonnes
Likely delivery
tipper or grab lorry
- 9.67 tonnes needs a tipper or grab lorry. Confirm access width, overhead clearance and where the driver can tip.
- Check that the delivery route can take the weight — block paving, drainage covers and soft verges are easily damaged.
Note: Approximately 2 pallets of paving
Safety and compliance
Material planning only
This estimate is for material planning only. Structural dimensions, foundations and compliance requirements should be checked by a qualified professional.
Two-person lift
Each paving slab weighs about 28 kg. Anything over 25 kg is a two-person lift, and large-format slabs need suction lifters to place accurately.
Check for buried services before digging
Before digging, check for buried services. Free utility plans are available from the relevant network operators, and a cable avoidance tool (CAT) scan is strongly recommended.
Data behind this estimate
| Assumption | Value | Source |
|---|---|---|
MOT Type 1 sub-base Graded crushed rock to the Series 800 specification. | 2,000 kg/m³range 1,900–2,100 | National Highways (UK)Reviewed 2026-07-01 |
Compaction allowance for granular sub-base Order about 30% more loose material than the finished compacted depth. | 1.3 × loose volumerange 1.2–1.4 | National Highways (UK)Reviewed 2026-07-01 |
Sharp sand / concrete sand Damp sand bulks up in volume but the delivered weight is what you pay for. | 1,600 kg/m³range 1,500–1,700 | Mineral Products AssociationReviewed 2026-07-01 |
Sand required per m³ of 1:5 mortar Allows for bulking; damp sand delivered by weight is the practical ordering unit. | 1.6 tonnes/m³range 1.5–1.7 | British Standards InstitutionReviewed 2026-07-01 |
Default waste allowance Covers cutting, breakage, setting-out error and the odd unusable unit. | 10 %range 5–15 | Project EstimateReviewed 2026-07-01 |
Cost
Enter the prices your supplier quoted. This site does not hold or estimate supplier prices, so totals appear only once you fill these in.
UK standard-rate VAT is 20%. Builders' merchant prices are often quoted excluding VAT.
No prices entered yet. Everything else in this estimate — quantities, weight, delivery and the shopping list — works without them.
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How this calculator works
Every figure below is derived rather than looked up, so you can check it against your own numbers. Nothing is hidden behind a black box.
Unit count
Paving is counted by module, not by slab. A 600 × 600 mm slab with a 10 mm joint occupies a 610 × 610 mm module, so it covers 0.3721 m² rather than 0.36 m².
Ignoring the joint over-orders by about 3% on a 10 mm joint and by more on small units — which is why block paving calculations go wrong most often.
units = area ÷ ((unit length + joint) × (unit width + joint))
Pattern and waste
Each pattern carries a recommended minimum waste allowance: 5% for a straight grid, 7% for running bond, 10% for basket weave and 15% for herringbone, where every perimeter unit is a diagonal cut.
If you set a lower allowance than the pattern justifies, the estimate says so rather than quietly under-ordering.
Random-size packs
Mixed-size packs are estimated from the coverage printed on the pack, because the size mix differs between suppliers and no calculator can predict a layout for them. The estimate says this plainly instead of inventing a plan.
Bedding
A full mortar bed is converted to sand and cement at a 1:5 ratio, using 1.6 tonnes of sand and 320 kg of cement per cubic metre of mortar.
A sand screed carries a 1.1 compaction allowance because it consolidates under the plate compactor.
Jointing
Joint volume is derived from geometry: the proportion of the surface that is joint rather than slab, multiplied by the depth of the unit.
For a 600 mm slab with a 10 mm joint that is 3.3% of the area; for a 200 × 100 mm block with a 3 mm joint it is 4.4%. Small units need proportionally more jointing material, not less.
joint volume = area × (1 − unit area ÷ module area) × unit thickness
Common questions
- How many paving slabs do I need?
- Divide the patio area by the module area of one slab — that is the slab size plus one joint width in each direction — then add a waste allowance for cuts. A 20 m² patio in 600 × 600 mm slabs with 10 mm joints needs 54 slabs before waste, and 60 with a 10% allowance.
- How deep should a patio sub-base be?
- 100 mm of compacted sub-base for a pedestrian patio on firm ground, 150 mm over soft or clay subsoil, and 150–200 mm if vehicles will cross it. Remember to order roughly 30% more loose material than the compacted depth.
- How much waste should I allow for paving?
- 5% for a straight grid on a rectangular area, 10% for most real patios, and 15% or more for herringbone, circular features or any area with angled edges.