Average bedroom walls
A 4m × 3.5m room with 2.4m ceilings, one door and one standard window has about 33m² of paintable wall area.
At 12m²/L for two coats, it needs 5.5L. With a 10% allowance, plan for about 6.1L.
Paint Calculator NZ: How Much Paint Do I Need?
Calculate how many litres of paint you need for an interior room, exterior walls, a fence or a roof in New Zealand. Include doors, windows, coats, product coverage, an optional waste allowance, primer, common tin sizes and an estimated paint cost.
Last reviewed by NZ Calculator: 5 July 2026 · Calculator takes about 1 minute
- The calculator converts your measurements into paintable area, litres and a practical tin combination.
- Enter the coverage rate printed on your chosen product label or technical data sheet for the best estimate.
- Coverage varies by paint, surface texture, porosity, application method and preparation, so use the result as a planning estimate.
How to calculate how much paint you need
Quick answer: As a planning range, many smooth-surface interior paints cover roughly 10–16m² per litre for one coat. The actual spreading rate depends on the product, surface condition and application method, so use the rate on the tin or technical data sheet.
Paintable area:Gross surface area − doors and windows + any included ceiling area
Topcoat litres:(Paintable area ÷ coverage rate in m²/L) × number of coats
Planning quantity:Topcoat litres × (1 + selected allowance percentage)
Resene publishes the same core formula: surface area divided by spreading rate, multiplied by the number of coats. The optional allowance in this calculator is user-controlled and is not a manufacturer requirement.
Your paint project
Uses 1.8m² per door.
Uses 1.2m² per window.
Add measured gables, extensions or wall sections not represented by the rectangular perimeter.
Resene publishes a 40% footprint allowance as a roof-paint rule of thumb.
Enter the spreading rate printed on the product label or technical data sheet.
Coverage quick picks
These are planning presets, not product promises. Actual rates vary by product and surface.
Check your measurements. Required dimensions and coverage rates must be greater than zero and within the permitted ranges.
Your paint estimate
Room estimateCalculating your paint estimate…
Calculated topcoat compared with the rounded purchase quantity. Primer is shown separately when selected.
Paintable area
0m²
Plan to buy
0L
| Gross measured surface | 0m² |
| Doors, windows or openings deducted | 0m² |
| Additional area included | 0m² |
| Net paintable area | 0m² |
| Topcoat calculation | 0L |
| After selected allowance | 0L |
| Primer calculation after allowance | 0L |
| Estimated paint cost | $0.00 |
| Total planned purchase quantity | 0L |
Common-pack planning guide
Topcoat best fit: —
Topcoat fewer tins: —
Primer best fit: —
Uses 10L, 4L, 2L and 1L as common planning sizes. Confirm the sizes sold for your chosen product.
How this Paint Calculator NZ works
The calculator first works out the surface area for the selected project. Room and exterior modes use the building perimeter multiplied by height. Fence mode uses length multiplied by height and the number of sides. Roof mode starts with the footprint and applies the selected pitch and corrugation allowance.
Doors, windows and other openings are deducted where relevant. The net area is divided by the topcoat coverage rate and multiplied by the selected number of coats. An optional allowance is then applied before the tool suggests practical pack combinations.
- Coverage rate matters most. Use the rate on the exact paint product rather than relying only on a general average.
- Two coats are common. Dulux states that its calculator assumes two topcoats, described as ideal for most Dulux paints.
- Porous and shaped surfaces need more. Resene warns that porous surfaces and shapes such as corrugated iron can require additional paint.
- Primer is separate. Select the primer option only when your paint system requires it, and enter the correct primer spreading rate.
Common paint estimating mistakes
This calculator is suitable for homeowners, landlords, DIY renovators, property managers and trade professionals preparing an initial paint estimate.
- Calculating only one coat. Many projects require two topcoats, and new or strongly contrasting surfaces may need a separate primer or additional coat.
- Using a generic coverage rate. The spreading rate can change by product, substrate, texture and application method, so use the selected paint's label or technical data sheet.
- Forgetting ceilings, gables or both sides of a fence. Include every surface that will receive the same coating system.
- Ignoring rough or porous surfaces. Bare timber, masonry, textured cladding and corrugated profiles can use more paint than a smooth flat-area estimate.
- Deducting openings inaccurately. Measure large doors, windows, gates and unpainted sections instead of relying only on standard opening sizes.
- Forgetting primer or sealer. New, repaired, stained or porous surfaces may need a separate preparation coat.
- Buying the exact theoretical litres. Pack sizes, touch-ups, colour change, application loss and future repairs can justify a sensible planning allowance.
NZ paint coverage guide
Coverage is product-specific. The following figures are examples published by New Zealand manufacturers and should help you choose a starting point before entering the exact rate from your tin or data sheet.
| Source or example | Published coverage | How to use it |
|---|---|---|
| Dulux general wall, trim or ceiling guide | About 16m²/L | A smooth-surface reference only; check the selected product. |
| Dulux general primer guide | About 14m²/L | A starting point for the optional primer field. |
| Resene SpaceCote worked example | 11m²/L | Shows why the product data sheet should determine the rate. |
| Resene professional planning average | 10m²/L per coat | A conservative estimate that allows for colour, waste and losses. |
| Wattyl wall topcoat example | 16m²/L | Worked example for previously measured interior walls. |
| Wattyl ceiling topcoat example | 14m²/L | Worked example for a ceiling surface. |
Coverage can fall below a theoretical rate on rough, porous, weathered or highly profiled surfaces. Application method, colour change, preparation and film thickness can also affect actual consumption.
Worked paint-calculation examples
Exterior house walls
A 12m × 8m rectangular house with 2.7m walls, two doors and eight standard windows has about 94.8m² of wall area before any gable addition.
At 10m²/L for two coats, it needs 19.0L. With a 10% allowance, plan for about 20.9L.
Corrugated roof estimate
A 10m × 8m footprint with a 40% pitch and corrugation allowance produces an estimated surface area of 112m².
At 10m²/L for two coats, it needs 22.4L before any separate user-selected allowance.
Choosing the right paint-calculator mode
Interior room paint calculator
Use Room mode for four walls in a rectangular room. It deducts standard doors and windows and can add the ceiling area. Calculate separate rooms independently when wall heights, colours or products differ.
Exterior house paint calculator
Use Exterior mode for rectangular wall perimeters. Add measured gable or extra wall area separately. This mode estimates wall paint only and does not automatically include soffits, trim, doors or window frames. For an outdoor project that also includes timber boards, use the Decking Calculator NZ to estimate deck materials separately.
Fence paint calculator
Use Fence mode for a flat length and height. Select one side or both sides. Slatted, rough-sawn or highly textured fencing may use more paint than the flat-area calculation suggests.
Roof paint calculator NZ
Use Roof mode for an early estimate based on the building footprint. Resene publishes a rule of thumb of footprint area plus about 40% for pitch, corrugations and soffit overhang. Trough-section roofing can need significantly more, so confirm the roof profile and coating system. Use the Roofing Calculator NZ when you also need roof-area and roofing-material estimates.
How the paint cost estimate works
Enter your own price per litre because retail prices, trade prices, pack-size discounts and promotional offers change. The calculator applies that price to the planned purchase litres rather than the unrounded theoretical amount.
A paint-only estimate does not include preparation products, filler, masking materials, brushes, rollers, spray equipment, scaffolding, labour or disposal. Primer cost is added only when primer is selected and a primer price is entered.
Businesses preparing a customer quote can calculate tax-inclusive and tax-exclusive totals separately with the GST Calculator NZ.
Official New Zealand paint guidance used
The calculator method and guidance were checked against manufacturer resources. Product labels and technical data sheets remain the best source for the exact paint system, spreading rate and number of coats.
How to use the Paint Calculator NZ
- Choose the project. Select Room, Exterior, Fence or Roof.
- Enter measurements. Use metres and include doors, windows or openings where relevant.
- Enter the topcoat details. Add the number of coats and the spreading rate from the product label.
- Choose an allowance. Use zero when you want only the theoretical quantity, or select an extra planning margin.
- Add primer when needed. Enter the separate primer coverage rate and optional price.
- Review the result. Check the calculated litres, rounded pack guide, assumptions and estimated paint cost.
Paint Calculator NZ frequently asked questions
A 4m by 3.5m bedroom with 2.4m-high walls, one standard door and one standard window has about 33m² of paintable wall area. At 12m² per litre for two coats, it needs about 5.5 litres before any extra allowance.
Divide the net paintable area by the product coverage rate and multiply by the number of coats. For example, 42m² divided by 12m² per litre and multiplied by two coats equals 7 litres.
It depends on the product and surface. Dulux publishes a general guide of about 16m² per litre for wall, trim or ceiling paint, while Resene examples include 11m² per litre and a conservative professional planning average of 10m² per litre per coat. Use the rate on the actual product.
Two topcoats are common, and Dulux describes two coats as ideal for most of its paints. The required system can differ for new, porous, stained or strongly contrasting surfaces, so follow the product label and preparation instructions.
Yes, when they will not be painted with the same product. Room and exterior modes deduct 1.8m² per standard door and 1.2m² per standard window. Measure unusually large openings separately for a more accurate estimate.
Multiply the building perimeter by the average wall height, add measured gable or extra wall area, and subtract doors and windows. Divide by the selected exterior paint coverage rate and multiply by the number of coats.
Multiply fence length by fence height and by the number of sides being painted. Deduct any gates or openings, divide by the paint coverage rate and multiply by the number of coats.
For an early estimate, Resene suggests using the roof footprint plus about 40% for pitch, corrugations and soffit overhang. Divide the estimated roof area by the product coverage rate and multiply by the number of coats. Complex or trough-section roofs need a more detailed measurement.
The calculator plans combinations using 10L, 4L, 2L and 1L sizes. Actual pack sizes vary by brand, product and retailer, so confirm availability before buying. The best-fit option minimises planned overbuy, while the fewer-tins option prioritises fewer containers.
Yes. Enter your own topcoat price per litre and, if relevant, primer price per litre. The result estimates paint cost using the rounded planned purchase quantity. It does not include labour, tools, preparation materials or access equipment.
It can provide an early quantity estimate for simple measured surfaces, but commercial projects may need separate calculations for different substrates, products, colours, access conditions and specified coating systems. Use project documents and manufacturer data for final procurement.
This calculator provides a planning estimate only. Actual paint consumption can differ because of product formulation, film thickness, surface texture and porosity, colour change, preparation, application method, overspray, weather and workmanship. Confirm the coating system, spreading rate, number of coats and pack sizes using the selected product label or technical data sheet.