Paint Calculator

How to Use Our Paint Calculator M2

Our paint calculator takes the guesswork out of budgeting for your next project. Start by selecting whether you’re painting an interior room or an exterior area. For interior spaces, measure the width of one wall followed by its adjacent wall, then enter the ceiling height if your room is square, the width and length will be the same. For exterior jobs, add together the width of each wall you’re painting and enter the wall height separately. Once you hit “Calculate Paint,” the tool converts your measurements into square metres and works out exactly how many litres of paint you’ll need across walls, ceilings, undercoat, and trims along with an estimated cost based on current Perth retail prices.

Paint Coverage & Estimation Tips

A few factors decide how accurate your estimate turns out to be. Here’s what actually affects paint coverage on a real job.

Standard Coverage Rate Per Litre

Interior paints typically cover 10–14 square metres per litre on smooth, previously painted walls, while exterior paints cover slightly less around 8–10 square metres per litre due to weather-resistant formulations. For example, a 40m² exterior wall painted with two coats at 9m² coverage per litre will need roughly 8.9 litres. Our calculator applies these industry-standard rates automatically so you don’t have to work it out by hand.

Number of Coats Required

Two coats of topcoat is the standard for most residential jobs and gives you consistent colour and long-term durability. If you’re covering a dark colour with a lighter one, or painting bare or previously unpainted surfaces, budget for a third coat this can increase your total paint requirement by up to 50%.

Wall Condition & Surface Type Impact

Textured, rendered, or bare plaster surfaces absorb noticeably more paint than smooth, previously painted walls, sometimes 15–20% more. If your property has rough render, brick, or older chalky paintwork, it’s worth adding a small buffer above your calculator estimate, and a primer coat is strongly recommended to seal the surface first.

House Painting Cost Calculator — What Affects Your Estimate

Your final cost comes down to a combination of surface area, paint quality, and the type of project. Here’s a quick breakdown:

Surface Area & Number of Coats

The total square metreage across your walls, ceilings, and trims, multiplied by the number of coats, is the single biggest factor driving your total paint quantity and cost.

Paint Type

Our estimates use trusted, high-performance products Wash&Wear for interior walls, Weathershield for exteriors, and Aquanamel for doors and trims so your quote reflects paints built to last, rather than budget alternatives that need repainting sooner.

Interior vs Exterior Painting Costs

Exterior painting usually costs more per square metre than interior work, largely due to weather-resistant paint, additional surface prep, and access requirements like ladders or scaffolding. Selecting the correct option in the calculator ensures your recommendations and cost adjust accordingly.

Paint Calculator FAQs

How accurate is this painting calculator?

It’s built on standard industry coverage rates and current Perth retail paint prices, so it gives you a reliable working estimate. For an exact, guaranteed price that accounts for your property’s specific condition, request a formal quote below.

How many coats of paint do I need?

Two coats is standard for most jobs. Bare surfaces, major colour changes, or textured walls often need a third coat, which our calculator can factor into your total.

Does this calculator include labour cost?

No, this tool estimates paint materials only. For a full price including labour, prep, and site access, submit the quote form below and our Perth team will follow up within 24 hours.

How many litres of paint do I need for an average house?

A standard 3-bedroom Perth home typically needs 45–55 litres across walls, ceilings, and trims for two coats though this varies with house size, wall condition, and paint type.

What’s the average cost per litre of paint in Perth?

Prices vary by brand and finish, but our calculator uses up-to-date AUD retail estimates for trusted trade paints like Wash&Wear, Weathershield, and Aquanamel to keep your figure realistic.