Screed Calculator: Volume, Bags, Cement and Sand
Enter the floor size and thickness to see how many bags of pre-mixed screed to buy, or how much cement and sand to mix yourself. In the US this is often called a mortar bed or floor leveling.
Your estimate
Buy 49 bags
49 bags (80 lb) of pre-mixed mortar bed
- Floor area
- 168 sq ft
- Volume
- 1.04 cu yd (1.14 cu yd with waste)
- Pre-mixed screed
- 3,844 lb10% waste
Add a price per bag to see the cost.
How we got this: 168 sq ft × 2 in × 10.4 lb/sq ft per in × 1.10 = 3,844 lb, rounded up to whole bags.
Let screed dry before laying flooring: about 1 day per mm for the first 40 mm. Test moisture before wood or vinyl.
How the calculation works
- Volume. Floor area × thickness, plus 10% for an uneven base and spills.
- Pre-mixed bags. Area × thickness in mm × about 2.0 kg/m² per mm, divided by the bag weight and rounded up.
- Cement and sand. Dry materials shrink when mixed with water, so we multiply the volume by 1.33 and split it by the ratio. Cement weighs about 1,440 kg/m³, sand about 1,600 kg/m³.
Metric example: a 4 × 5 m floor at 50 mm is 1.0 m³. Pre-mixed, that is 2,200 kg with waste: 88 bags of 25 kg. Mixed 1:4 yourself, it is 17 bags of 25 kg cement and 1.87 tonnes of sharp sand.
Imperial example: a 12 × 14 ft floor at 2 in is 28 cu ft (1.04 cu yd). Pre-mixed with 10% waste, that is about 1,744 kg, or 49 bags of 80 lb.
Guides to save and share
Chart as a table: How many bags of floor screed do I need?
| Room | 1 1/2 in thick | 2 in thick | 3 in thick |
|---|---|---|---|
| 10 × 10 ft (bedroom) | 22 | 29 | 43 |
| 10 × 12 ft (kitchen) | 26 | 35 | 52 |
| 12 × 15 ft (living room) | 39 | 52 | 78 |
| 15 × 20 ft (open plan) | 65 | 86 | 129 |
| 20 × 25 ft (basement) | 108 | 143 | 215 |
How much waste should I add?
| Floor | Extra | Why |
|---|---|---|
| Level slab, small room | 5% | Spills and material left in the mixer. |
| Typical floor | 10% | Small dips in the base fill with extra screed. |
| Uneven base or falls to a drain | 15% | Thickness varies across the floor. |
Common mistakes
- Mixing too wet. Wet screed is easier to spread but weaker and slower to dry. Aim for a mix that holds its shape when squeezed.
- Going thinner than the minimum for the screed type. Thin unbonded and floating screeds crack.
- Forgetting the edge insulation strip around a floating screed.
- Laying flooring too soon. Screed needs weeks to dry; test moisture before laying wood or vinyl.
What else you'll need
- Screed rails or battens and a straightedge.
- A float and a steel trowel.
- A forced-action mixer or a heavy-duty paddle mixer.
- Damp-proof membrane, plus edge insulation strip and mesh for floating screeds.
- A spirit level or laser to set the finished height.
Frequently asked questions
How much screed do I need per square metre?
Pre-mixed screed uses about 2 kg per m² for every mm of thickness. A 50 mm screed needs about 100 kg per m², which is 4 bags of 25 kg.
How thick should a floor screed be?
Under British Standard BS 8204-1: at least 25 mm for a bonded screed, 50 mm for an unbonded screed on a membrane, and 65 mm for a floating screed over insulation (75 mm for heavy loads).
What is the right sand and cement ratio for screed?
A 1:4 cement to sharp sand mix by volume is the usual floor screed. Use 1:3 for a stronger, thinner screed and 1:5 for thick, lightly loaded fills.
How long does screed take to dry?
A common rule is 1 day per mm for the first 40 mm, and slower after that, so a 50 mm screed takes around 7–8 weeks in good conditions. Always test moisture before laying flooring.
Screed or self-leveling compound: which do I need?
Use screed for layers of 25 mm (1 in) and more. For thin layers under about 10 mm (3/8 in), self-leveling compound is faster and easier.
How many bags of screed are in a cubic metre?
At about 2,000 kg per m³, a cubic metre of pre-mixed screed is about 80 bags of 25 kg, before waste.
Related calculators
This is an estimate. Actual use depends on the material, the surface, the installation method, waste and site conditions. Check quantities with your supplier before you buy.