How to Calculate Paint Quantity for a House (Interior & Exterior)

By Vystra · 13 August 2026

Paint is one of the last spends on a project — and one where over-ordering is common because coverage varies by surface. Here's how to estimate it properly.

Step 1 — Paintable area

For each wall: length × height. Add all walls and ceilings, then subtract doors and windows (roughly 20 sq ft per door, 15 per window).

Step 2 — Coverage and coats

• One litre of emulsion covers 120–140 sq ft per coat.
• Standard finish = 1 primer + 2 coats.

Worked example (1000 sq ft wall area)

• Two coats = 2000 sq ft of coverage.
• 2000 ÷ 130 ≈ 15 litres of emulsion.
• Plus primer ≈ 7–8 litres.

Surface matters

• New plaster drinks more primer.
• Rough/textured surfaces reduce coverage.
• Dark to light colour changes may need an extra coat.

Tie paint to the project

Painting is often subcontracted per sq ft, so material and labour need to reconcile against the same area. Vystra lets you log paint purchases and painter wages against the project — so the finishing stage doesn't quietly eat your margin.

Frequently asked questions

How much paint is needed for 1000 sq ft?

For 1000 sq ft of wall area with two coats, you need roughly 8–9 litres of emulsion, plus primer, since one litre covers about 120–140 sq ft per coat.

How many coats of paint are standard?

One coat of primer plus two coats of finish paint is standard for a good, even result on interior and exterior walls.

How do I calculate paintable wall area?

Multiply wall length by height for each wall, add them up, then subtract door and window areas.