What does the Plaster Calculator — Bags & Coverage do?

Calculate plaster needed in 25kg bags for skim coat, bonding/browning or one-coat plaster. All calculations are performed in your browser using official UK rates and thresholds.

Does this include waste allowance?

Yes. Most building material calculations include a standard 10% waste allowance. You can adjust this figure depending on the complexity of your project and cutting requirements.

Material prices are indicative estimates based on average UK prices. Actual costs vary by region, supplier, brand and current market conditions. Always get quotes from local suppliers.

Plaster Calculator — Bags & Coverage

Calculate plaster needed in 25kg bags for skim coat, bonding/browning or one-coat plaster.

Last updated: April 2026 · Source: GOV.UK — Building Regulations Approved Document C

Wall Height (m)

Wall Width (m)

Number of Walls

Doors/Windows (m²)

25kg Bags

Total Weight

86 kg

Wall Area

34.4 m²

Disclaimer

This calculator is provided for informational purposes only and should not be considered as financial or tax advice. All calculations are performed locally in your browser — no personal data is collected or sent to our servers. Rates and thresholds are sourced from HMRC and GOV.UK and are updated for the current tax year. Always verify results with HMRC or consult a qualified professional before making financial decisions.

How It Works

Plaster coverage depends on the product type and application thickness. Multi-finish plaster (the most common top coat) covers approximately 10–11 m² per 25 kg bag at 2 mm thickness. Bonding coat (base coat for solid walls) covers about 3.5 m² per 25 kg bag at 8 mm thickness. Browning (base coat for brick) covers a similar area.

This calculator takes wall and ceiling areas, subtracts openings, and calculates bags needed based on the plaster type and coat thickness. For a full re-plaster on brick, you typically need a base coat (8–11 mm) plus a finish coat (2 mm). For skim-coating existing plasterboard, only the finish coat is needed (2–3 mm).

Enter the area, plaster type and number of coats. The calculator shows bags of plaster, litres of PVA (for sealing surfaces before plastering) and approximate cost. One 25 kg bag of multi-finish costs around £8–12. For large areas, always mix from the same batch to avoid colour variations.

Example: Room walls 36 m² (less openings), skim coat only

Net wall area: 36 m²
Multi-finish at 2 mm: 36 ÷ 10.5 = 3.4 bags
Round up: 4 bags × 25 kg multi-finish
PVA: ~5 litres for surface preparation

Source: GOV.UK — Building Regulations Approved Document C

Frequently Asked Questions

What does the Plaster Calculator — Bags & Coverage do?: Calculate plaster needed in 25kg bags for skim coat, bonding/browning or one-coat plaster. All calculations are performed in your browser using official UK rates and thresholds.
Does this include waste allowance?: Yes. Most building material calculations include a standard 10% waste allowance. You can adjust this figure depending on the complexity of your project and cutting requirements.
Are prices accurate?: Material prices are indicative estimates based on average UK prices. Actual costs vary by region, supplier, brand and current market conditions. Always get quotes from local suppliers.