Wall Primer Quantity Calculator
Estimate wall primer litres from wall dimensions, doors and windows, manufacturer coverage, number of coats and practical application loss.
Primer inputs
Wall primer requirement
The wall primer quantity formula
Net area = gross wall area − openings
Base litres = net area × coats ÷ coverage
Planning litres = base litres × (1 + allowance)
Worked example
With 15 m of combined wall width and a 2.8 m height, gross area is 42 m². After 7 m² of openings, 35 m² remains. At 9 m²/L and one coat, the theoretical requirement is about 3.89 L; a 10% allowance raises it to about 4.28 L.
Why surface condition matters
New plaster, repaired areas and highly porous substrates may absorb more primer. Existing sound painted surfaces may behave differently. The product data and actual substrate condition should therefore guide the final quantity.
Doors and windows
Only deduct areas that will genuinely remain unprimed. Returns, reveals and edges may still require primer, so an overly broad opening deduction can understate material.
What this calculator does not decide
It does not select primer chemistry, determine substrate compatibility, specify number of coats or establish surface-preparation requirements.
Frequently Asked Questions
Can I deduct windows and doors?
Yes, for surfaces that will not receive primer.
Does porous wall material use more?
It can.
Should manufacturer coverage control?
Yes.
Can I calculate containers?
Yes.