Concrete, patios and shed bases: how much to order
Concrete is ordered in cubic metres: length times width times thickness, plus a margin for an uneven sub-base. A 3 x 3 m slab 100 mm thick needs 0.99 m³ with 10% extra. Mixed by hand at 1:2:4 that is 13 bags of cement (25 kg), 0.70 tonnes of sharp sand and 1.31 tonnes of 20 mm aggregate; above about a cubic metre, ready-mix or a mix-on-site lorry is usually less work.
This page gathers every UK calculator and guide we have on concrete and the hard landscaping that sits on a concrete or MOT Type 1 base: shed bases, patios, block paving, gravel drives and floor screed.
Concrete for common slab sizes
Worked out by the concrete calculator at 1:2:4 with 10% extra. 100 mm suits paths, patios and shed bases; drives and workshop floors are usually thicker.
| Slab (metres) | m³ at 100 mm | Cement bags at 100 mm | m³ at 150 mm | Cement bags at 150 mm |
|---|---|---|---|---|
| 2 x 2 | 0.44 | 6 | 0.66 | 9 |
| 3 x 2 | 0.66 | 9 | 0.99 | 13 |
| 3 x 3 | 0.99 | 13 | 1.48 | 19 |
| 4 x 3 | 1.32 | 17 | 1.98 | 26 |
| 4 x 4 | 1.76 | 23 | 2.64 | 34 |
| 5 x 4 | 2.20 | 28 | 3.30 | 42 |
| 6 x 5 | 3.30 | 42 | 4.95 | 63 |
Mix it yourself or order ready-mix?
A cubic metre of concrete weighs about 2.4 tonnes, all of which you shovel, mix and barrow. Hand mixing (or a hired mixer) suits a shed base or a few post holes. For anything larger, compare a ready-mix delivery, including the part-load charge on small orders, with a mix-on-site lorry that only charges for what it pours.
Shed bases
A 2.4 x 1.8 m shed base 100 mm thick on 100 mm of MOT Type 1 needs 0.48 m³ of concrete (7 bags of cement), 1.05 tonnes of MOT Type 1 and 8.4 m of shuttering board. The shed base calculator lists all of it for your size.
Patios and paving
A slab patio sits on compacted MOT Type 1 with a sharp sand or mortar bed. A 4 x 3 m patio in 600 x 600 mm slabs takes 36 slabs, 2.77 tonnes of MOT Type 1 and 0.60 tonnes of sharp sand, plus 14 m of edging.
Block paving and gravel drives
Block paving needs a deeper sub-base than a patio, a laying course of sharp sand, edge restraints and kiln-dried sand brushed into the joints. Gravel drives are cheaper and permeable, which matters because a new impermeable front garden surface over 5 m² needs planning permission unless the water drains to a lawn or border.
Floor screed
Screed is a sand and cement mix, not concrete, laid over a slab to give a level finish. A 4 x 3 m floor at 65 mm takes 0.86 m³, about 12 bags of cement and 1.46 tonnes of sharp sand at 1:4.5.
Every calculator for this topic
Guides
- Common Mistakes Laying a Concrete Base (UK): Depth, Mix, WasteConcrete mistakes that leave you short. A 3 × 3 m base at 100 mm needs 0.99 m³ with 10% extra, and a 150 mm base needs 1.48 m³.
- Common Mistakes Laying a Patio (UK): Slabs, Base, JointsPatio mistakes: no waste, no fall, a thin base. A 4 × 3 m patio of 600 × 600 mm slabs takes 36 slabs with 10% extra, and 38 with 15%.
- Gravel or Block Paving Driveway? What Each Needs, 6 x 5 mCompare a gravel and a block paved driveway for a 6 x 5 m area: the materials, the groundwork, drainage rules and which suits your property.
- How Many Paving Slabs Do I Need? Slabs per m² Chart (UK)Slabs per m² for every common size, plus the MOT Type 1 sub-base and sharp sand a patio needs, with a worked 4 x 3 m example.
- How Much Concrete Do I Need? m³ and Bag Charts (UK)How many m³ of concrete a slab needs and how many 25 kg bags of cement to mix it yourself, with charts by slab size and thickness, and ready-mix.
- Sand and Cement Mix Ratios (UK): Concrete, Screed, Render and MortarA cubic metre of 1 : 2 : 4 concrete takes 317 kg of cement (13 bags), 0.7 t of sand and 1.3 t of aggregate. Mix ratios for each job and the amounts per m³.
- Block Paving Driveway: Blocks, Sub-base and Sand NeededHow many blocks, tonnes of MOT Type 1 and laying course sand a block paved drive needs, with a chart for common sizes and a guide to getting it right.
- Gravel Driveway: Tonnes of Stone and Materials Needed (UK)How much MOT Type 1 and gravel a driveway needs, with the membrane and edging, and a chart of tonnes for common drive sizes. Check the front garden rules.
- Patio Materials List UK: Slabs, MOT Type 1 and SandEverything to lay a 4 × 3 m paving slab patio: slabs, MOT Type 1 sub-base, sharp sand or mortar and tools, with quantities and a size chart for other patios.
- Floor Screed: How Much Sand, Cement or Ready-Mix Do I Need?How to work out the volume of a floor screed, with the sand and cement for a 1:4.5 mix or the bags of ready-mix, charts by room and depth, and drying times.
- Concrete Shed Base UK: How Much Concrete, Which Mix, What to BuyThe concrete, mix, cement, sand, aggregate and MOT Type 1 for a shed base, ready-mix or mixed yourself, with quantities for shed sizes from 6 × 4 to 12 × 8 ft.
Other guides that use these calculators: Edging Units and Concrete for a Driveway or Path (UK) · Common Mistakes Putting Up a Fence (UK): Posts, Panels, Gates · Common Mistakes When Tiling a Floor or Wall (UK): Waste, Grout · Decking or Paving for a Garden? What Each Needs, 4 x 3 m · Drain Fall and Gradient: How Much Fall Does a Drain Need? (UK) · How Big a Water Butt Do I Need? Roof Area, Rainfall and Litres (UK) · How Many Feather Edge Boards Do I Need? Closeboard Fence (UK) · How Much Gravel Do I Need? Tonnes, Bulk Bags and Coverage (UK) · How Much Sand and Cement to Render a Wall? Bags and Tonnes (UK) · Decking Materials List UK: Boards, Joists and Screws
Answers for common sizes
Already know the size? These pages give the worked answer for one common size each, with the inputs filled in so you can adjust them.
Project planners
Planning the whole job rather than one material? These step-by-step planners put the calculators above in the order you will need them.
Frequently asked questions
How much concrete for a 3 x 3 m slab?
0.99 m³ at 100 mm thick, including 10% extra. At 1:2:4 that is 13 bags of cement, 0.70 tonnes of sharp sand and 1.31 tonnes of aggregate.
What mix should I use for a shed base?
A general-purpose 1:2:4 mix (cement, sharp sand, 20 mm aggregate) is the usual choice for paths, patios and shed bases. Use the stronger 1:1.5:3 for drives.
How thick should a shed base be?
100 mm of concrete on a compacted sub-base suits most garden sheds. Workshops and heavy loads are usually given 150 mm.
Do I need planning permission for a new driveway?
Not if it is permeable, or if rainwater runs to a lawn or border. Covering more than 5 m² of front garden with an impermeable surface that drains to the road needs permission in England.
Related topics
Estimates only. Quantities depend on your materials, site and supplier, so check pack sizes and coverage on the label. Check the Building Regulations and any planning rules for anything structural or close to a boundary. How we calculate.