Plastering Calculator UK | How Much Plaster Do I Need?
Free UK plastering calculator. Work out how many bags of plaster, sheets of plasterboard and rolls of scrim tape you need from your room dimensions.
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Results are estimates only and may vary depending on site conditions, material specifications and waste. EasyEstimate and its affiliates accept no responsibility for any loss or damage arising from reliance on these figures. Always verify quantities with your supplier before ordering.
How to Calculate Plaster and Plasterboard Quantities
Getting plaster quantities right means fewer trips to the merchant and less waste on site. This guide covers the calculations for skim coats, undercoats, plasterboard and accessories.
The Formulas
Wall area:
- Wall area = (wall 1 length + wall 2 length + wall 3 length + wall 4 length) × ceiling height
- Subtract window and door openings
Plaster bags:
- Skim coat (multi-finish, 2mm): Wall area ÷ 10.5 = bags of 25kg plaster
- Undercoat (bonding, 8mm): Wall area ÷ 3.5 = bags of 25kg plaster
Plasterboard sheets:
- Sheets needed = Wall area ÷ board area (typically 2.88 m²)
- Add 10% for waste and cuts
Plaster Coverage Table
| Plaster Type | Thickness | Coverage per 25kg bag | Common Use |
|---|---|---|---|
| Multi-finish (skim) | 2mm | 10–12 m² | Final coat over plasterboard or undercoat |
| Bonding coat | 8mm | 3.5 m² | Undercoat on low-suction backgrounds |
| Browning | 11mm | 2.5 m² | Undercoat on brick/block walls |
| Hardwall | 11mm | 2.5 m² | High-impact undercoat |
| One coat | 13mm | 2.0 m² | Direct to brick/block (no skim needed) |
| Board finish | 2mm | 10–12 m² | Skim coat specifically for plasterboard |
Plasterboard Sizes
| Board Size | Area | Weight (12.5mm) | Common Use |
|---|---|---|---|
| 2400 × 1200mm | 2.88 m² | 22 kg | Standard walls |
| 1800 × 900mm | 1.62 m² | 15 kg | Tight spaces, easier handling |
| 3000 × 1200mm | 3.60 m² | 27 kg | Taller walls, fewer joints |
| 2400 × 900mm | 2.16 m² | 16.5 kg | Ceilings (lighter) |
Worked Example: Standard UK Room (3m × 4m × 2.4m)
Full board and skim (new stud walls):
- Wall area = (3 + 4 + 3 + 4) × 2.4 = 33.6 m²
- Subtract openings: 1 door (0.8 × 2.0 = 1.6 m²) + 1 window (1.2 × 1.2 = 1.44 m²) = 3.04 m²
- Net wall area = 33.6 − 3.04 = 30.56 m²
- Plasterboard: 30.56 ÷ 2.88 = 10.6 → 12 sheets (with waste)
- Skim plaster: 30.56 ÷ 10.5 = 2.9 → 3 bags multi-finish (25kg)
- Scrim tape: Total joint length ≈ 30 lm → 1 roll (90m)
- Plasterboard screws: Approximately 12 per board → 144 screws (1 box)
Skim only (over existing plaster):
- Net wall area = 30.56 m²
- Skim plaster: 30.56 ÷ 10.5 = 3 bags multi-finish (25kg)
- PVA: 1 litre per 20 m² = 2 litres (diluted 1:4)
Ceiling Plastering
For ceiling work, the calculation is simpler:
- Ceiling area = Room length × room width
- Plasterboard: Use 9.5mm board. Sheets = ceiling area ÷ board area
- Skim: Bags = ceiling area ÷ 10.5
For the example room: Ceiling = 3 × 4 = 12 m² → 5 sheets of 9.5mm board + 2 bags of multi-finish.
Accessories Checklist
| Item | Quantity Rule |
|---|---|
| Scrim tape (90m roll) | 1 roll per 25–30 m² of board |
| Angle bead (2.4m length) | 1 per external corner |
| Stop bead (2.4m length) | 1 per edge where plaster meets another surface |
| PVA (5L) | 1L per 20 m² (diluted for bonding) |
| Plasterboard screws | 12 per standard board |
| Plasterboard adhesive (dabs) | 1 bag per 3–4 boards (dot & dab method) |
From Plastering Quantities to a Full Estimate
This calculator gives you material quantities. A full plastering estimate also includes:
- Labour (typically £150–200/day for a plasterer in 2026)
- Preparation (hacking off old plaster, making good)
- Access equipment (hop-ups, trestles for ceilings)
- Skip hire if stripping old plaster
EasyEstimate’s plastering calculator handles all of these with live UK material prices and labour rates — producing a complete, priced schedule in minutes.
Try the full plastering calculator free →
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Frequently Asked Questions
- How many bags of plaster per square metre?
- For skim coat (finish plaster), one 25kg bag of multi-finish covers approximately 10–12 m² at 2mm thickness. For bonding coat (undercoat), one 25kg bag covers approximately 3.5 m² at 8mm thickness. Always add 10% for waste.
- How many sheets of plasterboard per room?
- Divide each wall area by the board area. Standard plasterboard is 2400×1200mm (2.88 m²). For a room with 4 walls of 3m × 2.4m each, that's 28.8 m² ÷ 2.88 = 10 boards, plus waste. Subtract window and door openings.
- What thickness of plasterboard should I use?
- 12.5mm is the standard for walls in the UK. 9.5mm is used for ceilings. 15mm is required for certain fire and sound ratings. Moisture-resistant board (green) should be used in bathrooms and kitchens.
- How much does it cost to plaster a room in 2026?
- A typical UK room (3m × 4m) costs £400–600 to skim over existing plaster, or £800–1,200 for full board and skim including materials. Prices vary by region — London is typically 30–50% higher than the national average.
- What's the difference between bonding, browning and multi-finish plaster?
- Bonding is an undercoat plaster for low-suction surfaces (concrete, plasterboard). Browning is an undercoat for high-suction surfaces (brick, blockwork). Multi-finish is the final skim coat applied over either undercoat at 2–3mm thickness.
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