Work out flooring packs
Laminate, LVT or engineered boards. Pack size is on the box label.
Skirting and scotia
Underlay on the net area plus 5% for overlaps and trimming. Skirting and scotia get 10% extra for mitres and offcuts.
Sand and cement screed
Uses the room area above. Traditional screed is cement and sharp sand, nominally 1:4 by weight.
Quantities are estimates for ordering. Follow the flooring and screed manufacturer's instructions.
Screed quantities and minimum thickness
Per square metre, for pricing and checking.
| Depth | m³/m² | kg/m² | 25 kg premix | Cement bags 1:4 | Sharp sand t 1:4 |
|---|---|---|---|---|---|
| 25 mm | 0.025 | 50 | 2.0 | 0.40 | 0.040 |
| 40 mm | 0.040 | 80 | 3.2 | 0.64 | 0.064 |
| 50 mm | 0.050 | 100 | 4.0 | 0.80 | 0.080 |
| 65 mm | 0.065 | 130 | 5.2 | 1.04 | 0.104 |
| 75 mm | 0.075 | 150 | 6.0 | 1.20 | 0.120 |
| 100 mm | 0.100 | 200 | 8.0 | 1.60 | 0.160 |
Mix by weight, cement : sharp sand. Water not included.
| Screed | Minimum | Specify |
|---|---|---|
| Bonded | 25 mm | 40 mm |
| Unbonded (on a membrane) | 50 mm | 70 mm |
| Floating (on insulation) | 75 mm | 65 mm domestic |
“Specify” allows for deviations in the base. 65 mm is normally considered satisfactory for floating screeds in domestic housing.
How to work out flooring
Floor area = length × width; split L-shaped rooms into rectangles and add them. Add waste, divide by the m² per pack on the box and round up to whole packs.
- 5% for a simple rectangular room laid straight.
- 10% for rooms with lots of cuts, angles or a diagonal lay. Many fitters use 10% as standard.
- 15–20% for herringbone and chevron.
Example: 4.5 × 3.6 m = 16.2 m², plus 5% = 17.0 m². With 2.0 m² packs that is 9 packs.
Underlay, skirting and scotia
Underlay goes on the net floor area with a little extra for overlaps — check the roll size, it varies by product. Some LVT and engineered boards have underlay attached or need a specific thin underlay, so follow the flooring manufacturer. Skirting and scotia run round the perimeter less the doorways; scotia beading is commonly sold in 2.4 m lengths. Leave the expansion gap the flooring manufacturer specifies.
Screed
Volume = area × depth. A traditional cement and sharp sand screed weighs roughly 1,800–2,000 kg/m³, so each 10 mm of depth is about 18–20 kg per m². The nominal mix is 1:4 cement to sharp sand by weight, within limits of 1:3 to 1:4.5 (BS 8204-1). Example: 16.2 m² at 65 mm = 1.05 m³, about 2.1 tonnes — 85 bags of 25 kg pre-mix, or 17 bags of cement and 1.7 t of sharp sand at 1:4, before waste.
Questions floor fitters ask
How much extra laminate flooring should I buy?
Add about 5% for a simple rectangular room laid straight, 10% for rooms with lots of cuts or a diagonal lay, and 15–20% for herringbone. Round up to whole packs.
How many packs of flooring do I need?
Multiply the room length by the width, add the waste percentage and divide by the m² per pack on the box, then round up. A 4.5 × 3.6 m room with 5% waste and 2 m² packs needs 9 packs.
How much does sand and cement screed weigh per m²?
About 18–20 kg per m² for every 10 mm of depth, based on a density of roughly 1,800–2,000 kg/m³. A 65 mm floating screed is therefore around 120–130 kg per m².
What is the minimum thickness for a floor screed?
Under BS 8204-1 as summarised by the Mortar Industry Association: 25 mm bonded (40 mm recommended), 50 mm unbonded (70 mm recommended) and 75 mm floating, with 65 mm normally considered satisfactory for domestic housing.
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See Graftum estimatingQuantities are estimates for ordering. Follow the flooring and screed manufacturer's instructions.