Screed Calculator – Cement, Sand, Volume & Cost Estimator
Calculate screed volume, cement, sand, ready-mix quantity, wastage and project cost for floors, roofs and other surfaces with our professional screed calculator.
What is a Floor Screed?
A floor screed is a thin layer of material (typically a sand and cement mortar, anhydrite, or self-leveling compound) laid over a concrete subfloor to create a flat, smooth, and level surface ready for structural finishes such as tiles, wood, vinyl, or carpet. Beyond leveling, screeds are also used to encase underfloor heating pipes, provide drainage slopes on roofs/terraces, and distribute loads evenly on insulation boards.
How Screed Quantity is Calculated
Estimating screed materials relies on three key parameters:
- 1. Wet Volume (Vwet): Calculated by multiplying the total application surface area by the average thickness: V = A × T.
- 2. Dry Material Factor: Sand and cement lose volume when mixed with water and compacted. A factor (typically 1.33 to 1.40) is applied to find the equivalent dry bulk volume of constituents.
- 3. Mix Proportion Parts: For a standard 1:4 cement-sand screed, the dry volume is divided into 5 total parts (1 cement + 4 sand).
Wet Volume vs. Dry Volume
When water is added to a dry sand-cement mixture, the water fills the voids between the sand grains, causing the bulk volume to shrink. Compacting the screed on-site further reduces volume. To compensate for this shrinkage, engineers use a Dry Volume Factor (usually 1.33 to 1.40):
For example, 1.0 m³ of wet screed requires approximately 1.33 m³ of dry materials before mixing.
Common Floor Screed Systems
Screed laying methods depend on structural thickness constraints and insulation layers:
| Screed Type | Min. Thickness | Application Method |
|---|---|---|
| Bonded Screed | 15 mm to 40 mm | Bonded directly to concrete slab using bonding slurry/primer. |
| Unbonded Screed | 50 mm | Laid over a damp proof separation membrane (DPM) to isolate from slab. |
| Floating Screed | 65 mm (domestic) / 75 mm | Laid over insulation boards with separation membranes. |
Worked Estimation Example
Let's calculate the sand and cement required for a 100 m² floor with a screed thickness of 50 mm (0.05 m) using a 1:4 ratio and a dry factor of 1.33:
- 1. Wet Volume: 100.0 × 0.05 = 5.0 m³
- 2. Dry Volume: 5.0 × 1.33 = 6.65 m³ dry materials.
- 3. Cement Portion (1 part in 5): 6.65 × (1÷5) = 1.33 m³ of cement. Weight = 1.33 × 1440 kg/m³ = 1915 kg — approx. 38.3 bags of 50 kg.
- 4. Sand Portion (4 parts in 5): 6.65 × (4÷5) = 5.32 m³ of sand. Weight = 5.32 × 1600 kg/m³ = 8512 kg — approx. 8.5 tonnes.
Screed Calculator FAQs
Q. What mix ratio is best for floor screed?
A. A 1:3 or 1:4 cement-sand mix ratio by volume is most commonly used for traditional screeds. 1:4 is standard for domestic and commercial applications, providing a good balance between workability and compressive strength.
Q. How do I calculate screed for multiple rooms?
A. Our calculator features a Multi-Area grid where you can add as many rooms as needed (e.g., Bedroom, Living Room) with distinct dimensions and thicknesses. The engine aggregates these automatically into a combined total.
Q. How thick should a self-leveling screed be?
A. Self-leveling underlayment screeds are very thin, typically ranging from 3 mm up to 15 mm. Always check the manufacturer's technical data sheets for density, coverage, and maximum thickness limits.