Calculator Inputs
Formula Used
- Room mode: Gross Area = 2 × (Length + Width) × Height × (Walls Covered ÷ 4)
- Direct mode: Gross Area = Total Wall Area
- Net Area = max(0, Gross Area − Openings Area)
- Allowance Factor = 1 + Waste%/100 + Strength%/100
- Adjusted Area = Net Area × Allowance Factor
- Packs Needed = ceil(Adjusted Area ÷ Coverage per Pack)
- Total Powder (kg) = Packs × Powder per Pack
- Total Water (L) = Packs × Water per Pack
How to Use This Calculator
- Select a method: room dimensions or direct wall area.
- Choose units, then enter wall sizes and openings area.
- Set coverage per pack using your paste label.
- Add waste allowance for trimming and overlaps.
- Optionally add strength allowance for heavier coverings.
- Click Calculate and review packs, powder, and water.
- Use CSV or PDF buttons to save the estimate.
Example Data Table
| Scenario | Wall Area (m²) | Openings (m²) | Waste (%) | Coverage (m²/pack) | Estimated Packs |
|---|---|---|---|---|---|
| Garden office, light paper | 32.40 | 2.50 | 10 | 5.00 | 7 |
| Shed feature wall | 12.00 | 1.00 | 8 | 4.50 | 3 |
| Studio, heavy lining | 44.00 | 3.20 | 12 | 5.50 | 9 |
Coverage rate and pack sizing
Paste products vary by formulation and paper weight, so the coverage per pack is the key driver of cost and stock control. Enter the label coverage for your specific product and keep it consistent with your chosen units. The calculator converts common inputs to a single metric basis, then rounds packs up to avoid mid-job shortages.
Wall area and openings adjustment
Wall area can be estimated from room dimensions using perimeter and height, or entered directly when surfaces are irregular. Openings such as doors and windows should be subtracted as a total area to avoid over-ordering. If you plan to paper into reveals, reduce the opening deduction slightly to reflect those returns.
Waste and handling allowances
A waste allowance helps cover trimming, pattern matching, and paste losses during mixing and rolling. Ten percent is a sensible starting point for straight drops, while patterned papers and tight corners may need more. The extra strength option adds a controlled margin for heavier coverings or slightly porous walls.
Mixing water and batch control
Total powder and water are calculated from whole-pack quantities, making batching predictable on site. Measure water first, then add powder gradually to reduce lumps, and allow the resting time recommended on the label. For larger spaces, mix in consistent batches so viscosity remains stable across all lengths.
Example inputs for a garden workspace
Example data: length 4.0 m, width 3.0 m, height 2.7 m, openings 2.5 m², waste 10%, strength 0%, coverage 5.0 m² per pack, powder 0.20 kg per pack, water 0.80 L per pack. This produces an adjusted area near 35 m² and typically purchases 7 packs, depending on your exact product coverage rating.
FAQs
1) Should I use room dimensions or direct wall area?
Use room dimensions for rectangular rooms with standard walls. Use direct wall area when surfaces are segmented, sloped, or already measured from drawings. Both methods end with the same allowance and pack calculations.
2) How do I choose a realistic coverage per pack?
Use the manufacturer label for your paste type and paper weight. If you are unsure, start slightly conservative, then adjust after a small test area. Coverage changes with roller load and wall absorbency.
3) What waste percentage is typical?
Ten percent works for simple layouts. Pattern matching, corners, and complex reveals can push waste to 12–18%. For feature walls with many cuts, increase waste to reduce the risk of running short.
4) Why is there an extra strength option?
Heavier coverings, lining paper, or slightly porous substrates can require a thicker mix. The extra strength percentage adds controlled margin without guessing, helping maintain adhesion where conditions are less ideal.
5) Should openings always be subtracted fully?
Usually yes, but if you paper into window and door reveals, subtract a bit less to cover those returns. Also consider alcoves and columns as extra area rather than openings.
6) Why does the calculator round packs up?
Paste is typically sold as whole packs. Rounding up avoids shortages caused by trimming loss, viscosity adjustments, and label variance. Extra paste is useful for touch-ups and seam work during installation.
7) Can I work in feet and still get correct results?
Yes. Select feet and enter room sizes, areas, and coverage in feet-based units. The calculator converts everything internally to a consistent metric basis, then shows the final paste and water totals.