Paint Coverage Calculator (Construction Version)

Paint coverage calculator for estimating litres and cans for a construction paint job

This paint coverage calculator is built for one simple job: estimating how much paint to buy when you already know the total paintable surface area. That is the most common situation on real sites and refurbs because someone has measured the walls and ceilings, used plans, or received an area total from a quantity surveyor or estimator. The output you need is practical procurement: litres required, how many cans to buy, and an allowance so you do not run short mid-job.

To use it, enter the total area to be painted in square metres and the number of coats. The calculator applies a coverage rate (how many square metres one litre covers) and converts the result into litres. Then it applies a waste or extra allowance to account for real-world losses such as roller loading, tray residue, overspray, cut-in waste, absorption on rough surfaces, and touch-ups. Finally, it converts total litres into whole cans based on your chosen can size, rounding up because you can only buy whole containers.

The main result is the total litres to buy including your allowance, plus the recommended number of cans. You also get a breakdown showing the base litres before allowance and the extra litres added by the allowance. If you add a price per litre, the calculator estimates the total paint cost for budgeting. This page is intentionally limited to paint quantity planning and purchasing. It does not attempt to calculate wall area from room dimensions or to estimate primer, undercoat, or special coatings. Those are separate decisions with different assumptions and product rules.

Assumptions and how to use this calculator

• The total area you enter is the paintable surface area after subtracting exclusions you do not plan to paint (for example, large openings), unless you intentionally include them.
• Coverage rate is treated as an average in m² per litre. If you are unsure, use the default and increase the waste allowance for rough, porous, or previously unpainted surfaces.
• The waste allowance covers normal site losses and contingency. It does not replace a separate decision about primer, filler, or surface preparation.
• The calculator rounds up to whole cans because partial cans cannot be purchased. This can produce small leftover paint, which is usually better than running short.
• Results assume the same product and coverage across the whole area. If you are using multiple paints or very different surfaces, calculate each area separately and add the totals.

Common questions

What coverage rate should I use if I do not know the product spec?

Use a conservative default and treat it as an estimate. Many common interior and exterior paints land in a broad range depending on sheen, pigment load, and surface absorption. If you do not have a data sheet, keep the coverage rate at the default and increase the waste allowance. If the surface is rough, porous, or previously unpainted, a higher allowance is often the fastest way to avoid under-ordering without pretending you have precision.

Why does the calculator add a waste allowance instead of showing one exact number?

Because real painting rarely matches label coverage exactly. Losses come from cut-ins, roller loading, tray residue, overspray, touch-ups, and unavoidable spillage. Even when the painter is careful, coverage varies with technique, surface texture, temperature, and how much the surface absorbs. The allowance is a controllable lever that lets you trade cost versus risk of running short.

Should I include doors, windows, or trim in the area?

Only if you are painting them with the same paint and you want them included in the same purchase estimate. This calculator assumes one paint type and one coverage behaviour across the entire area. In many jobs, trim paint is a different product with different coverage and application method. If you are painting trim separately, exclude it from the area and run a separate calculation for that surface.

What if I only know the floor area, not the wall and ceiling area?

This calculator is not meant for that use case. Floor area does not translate reliably to paintable wall and ceiling area because it depends on ceiling height, room shape, openings, and whether ceilings are included. If you only have floor area, you need a different estimator that derives wall and ceiling area from dimensions. For this page, the intent is procurement when the paintable area is already known.

Why does the number of cans sometimes seem high compared to the litres?

The can count rounds up to the next whole container. If your total required litres is close to a can boundary, rounding can add a meaningful percentage. That is normal, and it usually reflects purchasing reality rather than a math error. If you want to reduce leftover, you can change the can size to match what your supplier sells (for example, mixing 5 L and 1 L cans), but this calculator intentionally keeps the decision simple by using one can size.