Calculator
Example data table
| Length (m) | Width (mm) | Thickness (mm) | Pieces | Surfaces | Coverage (m2/L) | Coats | Wastage (%) | Estimated liters |
|---|---|---|---|---|---|---|---|---|
| 3.600 | 150 | 50 | 24 | All faces | 6.00 | 2 | 8 | Approx 20.7 |
| 2.400 | 100 | 50 | 40 | Four sides | 7.50 | 2 | 10 | Approx 16.1 |
| 4.800 | 200 | 75 | 10 | Top + bottom | 5.00 | 3 | 12 | Approx 30.2 |
Examples are illustrative. Always verify product label coverage.
Formula used
Convert width and thickness to meters, then compute area per piece.
- All faces: A = 2(LW + LT + WT)
- Top + bottom: A = 2(LW)
- Four sides: A = 2(LT) + 2(WT)
- One face: A = (LW)
Use either coverage or application rate per coat.
- Total area: A_total = A_piece x pieces
- Application rate: r = 1 / coverage (if coverage given)
- Liters: L = A_total x r x coats x (1 + wastage%)
- Containers: ceil(L / container_size)
How to use this calculator
- Measure timber length in meters, and width/thickness in millimeters.
- Enter the number of pieces that need treatment.
- Select surfaces to coat, matching site exposure conditions.
- Use label coverage (m2/L) or enter an application rate (L/m2).
- Set coats and wastage to reflect absorption and handling losses.
- Pick a container size to round up purchase quantities.
- Press Submit to see results above the form.
- Download CSV or PDF for records and procurement.
Treatment coverage planning
Coverage varies by chemistry, timber species, and application method. Use label coverage for one coat on clean, dry wood. If you know liters per square meter, enter that rate directly. Align rates with brushing, spraying, rolling, or dipping. Higher viscosity products usually cover less. Moisture content above specification can reduce penetration and waste material.
Surface area drivers
Quantity depends on exposed surface area, not timber volume. A long, thin member may consume more preservative than a short, thick one. Select the faces you will coat, including cut ends where absorption is highest. Include rebates, notches, and drilled zones if present. Use a custom factor for partial or selective treatments on mixed assemblies.
Coat build and absorption
Each additional coat multiplies demand and improves retention. Rough sawn timber typically absorbs more, while planed faces absorb less. End grain, checks, and fastener holes increase uptake. Set coats to match specification, then adjust wastage to reflect timber condition, temperature, and drying time between coats. Wet-on-wet schedules can increase consumption compared with fully cured layers.
Wastage and procurement rounding
Wastage covers overlap, container residue, and handling losses. Use higher allowances for windy spraying, porous wood, and complex detailing. The calculator rounds up to whole containers for procurement. Compare required liters to purchased liters to manage leftovers. Plan batch sizes so partial containers are used on the next shift. Store product sealed to limit evaporation and contamination.
Documentation and site control
Record inputs, calculated area, and required quantity for inspection and quality control. Export the CSV for estimating logs, cost tracking, and material reconciliation. Use the PDF report for approvals, method statements, and toolbox briefings. Add product name, batch number, and application date in your site records. Consistent documentation reduces rework, supports compliance, and improves forecasting across multiple crews. When audits occur, show calculated quantities against invoices and usage notes. This evidence helps justify allowances, demonstrates controlled application, and supports durability expectations for timber in exterior exposure classes during long project lifecycles.
FAQs
Which coverage number should I enter?
Use the manufacturer coverage per coat in m2 per liter on prepared wood. If you have a measured application rate in liters per m2, enter that instead and leave coverage blank.
How do I treat only the ends and edges?
Choose Four sides for edges. For ends only, use Custom factor and enter a small fraction based on end area versus full area, then verify against your method statement.
Why does rough timber need more preservative?
Rough surfaces have more texture and open fibers, increasing absorption. Checks and end grain also pull in liquid. Increase wastage or reduce coverage to reflect that behavior.
What wastage percentage is typical?
For careful brushing on simple members, 5–10% is common. Spraying, porous species, or complex detailing may require 10–20%. Track actual usage and refine the allowance.
How are container quantities calculated?
The calculator divides required liters by container size and rounds up to whole containers. This provides a purchase quantity that avoids shortages, even when the exact requirement is not a full container.
Can I estimate mass for handling and lifting?
Yes. Enter product density in kg per liter to get an approximate mass. Use this for manual handling plans, but confirm final values from the product safety data sheet.