Sand and Cement Mix Ratios (UK): Concrete, Screed, Render and Mortar
The ratio of a mix is the number of parts of sand (and aggregate) for each part of cement, measured by volume. A general-purpose concrete is 1 : 2 : 4, a floor screed is about 4.5 : 1 and mortar and render are 4 : 1 to 6 : 1. One cubic metre of 1 : 2 : 4 concrete needs about 317 kg of cement (13 bags of 25 kg), 0.7 tonnes of sharp sand and 1.3 tonnes of 20 mm aggregate. The calculators work out your own job: concrete, screed and render.
Concrete (cement : sharp sand : 20 mm aggregate)
Per cubic metre of finished concrete:
| Mix | Use | Cement | Sharp sand | 20 mm aggregate |
|---|---|---|---|---|
| 1 : 2 : 4 | General purpose: paths, patios, bases | 317 kg (13 bags) | 0.70 t | 1.32 t |
| 1 : 1.5 : 3 | Stronger: slabs and drives | 403 kg (17 bags) | 0.67 t | 1.26 t |
| 1 : 3 : 6 | Weak: blinding and fill only | 222 kg (9 bags) | 0.74 t | 1.39 t |
Screed (sand : cement)
Per cubic metre of finished screed:
| Mix | Use | Cement | Sharp sand |
|---|---|---|---|
| 3 : 1 | Rich, bonded screed | 468 kg (19 bags) | 1.56 t |
| 4 : 1 | A stronger screed | 374 kg (15 bags) | 1.66 t |
| 4.5 : 1 | Typical floor screed | 340 kg (14 bags) | 1.70 t |
| 5 : 1 | A leaner screed | 312 kg (13 bags) | 1.73 t |
Render, mortar and bedding (building sand : cement)
Per cubic metre of finished render or mortar:
| Mix | Use | Cement | Building sand |
|---|---|---|---|
| 3 : 1 | Rich: a strong base coat | 468 kg (19 bags) | 1.56 t |
| 4 : 1 | General purpose render and mortar | 374 kg (15 bags) | 1.66 t |
| 5 : 1 | A finishing coat, or blockwork mortar | 312 kg (13 bags) | 1.73 t |
| 6 : 1 | A sheltered or internal wall, or paving bed | 267 kg (11 bags) | 1.78 t |
What the numbers mean
- By volume: a part is a volume, not a weight. Use a bucket or a shovel as the measure.
- Bulking: the dry sand and cement pack into a smaller volume when they are wetted, so a cubic metre of finished mix needs about 1.3 times that volume of dry materials (1.54 for concrete with aggregate).
- Weights: cement is about 1,440 kg per cubic metre, sharp and building sand about 1,600 and 20 mm aggregate about 1,500.
- Allow extra: add 5 to 15% for spillage, waste and uneven surfaces.
Choosing the mix
- Richer is not always better. More cement makes a stronger but more brittle mix that shrinks and cracks more.
- Match the job. A weak mix suits fill and blinding, a general mix suits paths and bases, and a stronger mix suits slabs and drives.
- Match the wall. Mortar and render should be no stronger than the bricks or the wall, so that cracks form in the joints and not in the bricks.
- Plasticiser: use a plasticiser rather than washing-up liquid to make mortar and render workable, and follow the maker's instructions.
For quantities of other materials see the brick calculator (with the mortar), the block calculator and the concrete guide. These are estimates: for structural work use the mix your engineer or supplier specifies.
Frequently asked questions
What is the mix ratio for concrete?
A general-purpose mix is 1 part cement to 2 of sharp sand and 4 of 20 mm aggregate (1 : 2 : 4). One cubic metre takes about 317 kg of cement (13 bags of 25 kg), 0.7 tonnes of sand and 1.3 tonnes of aggregate.
What is the mix ratio for mortar?
For bricklaying, 4 or 5 parts of building sand to 1 of cement (4 : 1 or 5 : 1), with a plasticiser. Use a weaker mix for soft bricks and a stronger one for exposed walls and engineering bricks.
What is the mix ratio for screed?
About 4.5 parts of sharp sand to 1 of cement for a normal floor screed, mixed fairly dry ("semi-dry"). A richer mix is used for a bonded screed.
What is the mix for render?
A 4 : 1 mix of building sand to cement is a general-purpose render, with a richer base coat and a leaner finishing coat.
How do I measure the parts?
By volume, using a bucket or a shovel as one part. Use the same bucket for the cement and the sand, and keep the sand damp but not wet.
More guides
Tools & materials for this project
Affiliate links As an Amazon Associate we earn from qualifying purchases. These links do not change what you pay.
Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and check the Building Regulations and any planning rules for anything structural or close to a boundary.