Measure painted surface, not floor area alone

For walls, add the length of every wall and multiply by average height. Add ceiling, door, trim or other surfaces that use the selected coating system. Subtract openings only where they will not be painted and where omitting them is worth the measuring effort.

A room with a 4 metre by 5 metre floor and 2.7 metre height has a wall perimeter of 18 metres and gross wall area of 48.6 square metres. The 20 square metre floor area does not describe the wall quantity. This calculator therefore asks for total wall length and height separately.

Different substrates and products should be run as separate scenarios. Walls, ceilings, doors, trim, masonry, metal and timber can need different primer, topcoat, coverage and labour. Combining everything under one premium wall-paint rate may produce inaccurate litres and pricing.

Coverage converts square metres and coats into litres

Dulux explains the basic paint formula as surface area divided by coverage rate per litre multiplied by the number of coats. Its calculator assumes two topcoats at a stated spread rate for its scenario, while product pages show that actual coverage differs by coating. Always use the chosen product’s current label and technical data.

The waste allowance can cover roller and brush loading, tray residue, texture, cutting-in and a small touch-up reserve. It should not be used to conceal unknown area. Spray application, rough masonry or very porous substrate can require a different allowance and professional method.

Rounding to whole tins creates leftover paint. The result multiplies whole tins by price, not exact litres by an average unit price. Primer remains a per-litre allowance because pack size and product were not entered; replace it with a supplier quote if material cost is important.

Preparation often controls durability and labour

A low-cost repaint over sound, clean coating differs from a project with peeling paint, failed sealant, water damage, chalking, mould, rust, movement cracks or rotten timber. Inspection should identify and remedy the cause before cosmetic work.

Preparation can include washing, masking, protection, scraping where safe, sanding where safe, filling, caulking, spot priming, stain blocking and surface-specific treatment. Product instructions govern compatibility, drying, temperature, moisture and recoat times.

The primer-area field supports spot priming or full priming. Enter 100% for an entirely primed surface and zero only where the coating specification supports no primer. One primer coat is assumed; specialised systems may require more and should be costed separately.

The fixed preparation allowance is useful while labour is quoted as one total, but avoid double counting. If painter hours already include all preparation, use the field only for repair materials or specialist subcontract work that sits outside those hours.

Check asbestos, lead and access before disturbing old coatings

NSW asbestos guidance says homes built before 1990 can contain asbestos and that even redecoration can disturb it. Suspected asbestos should not be sanded, scrubbed, water-blasted, cut or drilled. A licensed assessor can identify materials; if uncertain, stop and treat the material as asbestos until advised.

Asbestos cement in good condition may sometimes be sealed with suitable paint under safe guidance, but preparation methods are restricted. Do not insert ordinary sanding labour into the budget for a suspected surface. Add professional assessment and any licensed work as a separate scope.

Older paint can contain lead. Sanding and removal can create hazardous dust, especially for children and workers. Obtain jurisdiction-appropriate lead guidance, testing and controls. Spray coatings, solvents and isocyanates can introduce additional respiratory, fire and exposure risks.

Exterior work can involve ladders, scaffolds, elevated work platforms, roofs, power lines and public protection. The access field is a budget placeholder, not a safe-work plan. Contractors must assess and control risks under applicable work health and safety law.

Price labour from scope and productivity evidence

Hourly cost is not simply a worker’s wage. A contractor quote can include supervision, insurance, licences where required, travel, setup, administration, tools, warranty risk and profit. Enter the quoted effective hourly amount only when hours are a sensible way to compare.

Fixed-price quotes can be safer for a well-defined scope. Ask each painter to state preparation, number of coats, products, areas, exclusions, access, protection, cleanup, start and completion expectations and variation process. A much lower quote may omit work or use different material.

Occupied homes can take longer because rooms, furniture, pets and daily cleanup restrict sequencing. Empty new work may be faster but need more sealing and defect rectification. Exterior productivity changes with height, weather, masking and substrate detail.

Do not divide the final quote by floor area and assume that rate transfers to another house. Surface area, openings, trim, condition and access are the real drivers. Use the calculator to normalise those factors.

Select the coating system before buying paint

Confirm interior or exterior exposure, substrate, existing coating, sheen, washability, mould resistance, colour change and manufacturer preparation. Dark or vivid colour changes may need extra coats or a tinted undercoat. A product advertised as self-priming can still have substrate-specific limitations.

Buy enough matched paint for continuous areas and record batch details. Keep a labelled touch-up quantity only where safely stored. Colour appearance changes with lighting and sheen; sample first rather than treating opened custom-tinted paint as freely returnable.

Include fillers, sealants, masking, drop protection, rollers, brushes, trays, abrasives where safe, cleaning materials and disposal. The consumables field combines them for budget simplicity. A professional quotation may already include all of these.

Compare the result with quotes and budget

The central total adds contingency after all entered categories. Contingency covers genuinely unresolved minor quantity and condition risk. Known repair, access or hazardous-material work belongs in the base scope, not an optimistic contingency.

When the result exceeds budget, adjust specification or staging before reducing preparation. Skipping required preparation can shorten coating life and make the apparent saving expensive. Consider painting fewer rooms, simplifying colours or delaying nonessential areas while protecting weather-exposed surfaces.

Recalculate after the site inspection and colour or product selection. Attach the measurement and assumptions to quote requests. At completion, inspect agreed coats, coverage, edges, repairs, protection and cleanup under suitable light, then keep invoices and product records for warranty and maintenance.