Estimate the paint quantity
Paint · practical calculator
Running out of paint halfway across a wall is frustrating. Finishing with a whole unopened can is not much better. A useful estimate starts with the area you will actually paint, the number of coats and the coverage stated for the exact product—not the floor area or a universal online rule.
The coverage stated for the exact product matters more than a universal online assumption.
The calculator below does not hard-code one standard coverage figure for every paint. Check the label or technical data sheet and enter the coverage of the product you plan to use. Different paints can specify different coverage and different numbers of coats depending on the product and substrate.
Estimate the quantityUnitsMetric — m² / LImperial — ft² / US galTotal area (m²)Area not being painted (m²)Number of coatsProduct coverage (m²/L)Optional buffer (%)Calculateconst SQFT_PER_M2=10.7639104167,GAL_PER_L=0.2641720524,COVERAGE_IMPERIAL_PER_METRIC=SQFT_PER_M2/GAL_PER_L;let currentUnit='metric';function fmt(n){return Number(n).toLocaleString('en',{minimumFractionDigits:0,maximumFractionDigits:2})}function setNum(id,n){document.getElementById(id).value=Number(n.toFixed(4))}function switchUnits(){const next=document.getElementById('unitSystem').value;if(next===currentUnit)return;const gross=Number(document.getElementById('gross').value),openings=Number(document.getElementById('openings').value),coverage=Number(document.getElementById('coverage').value);if([gross,openings,coverage].every(Number.isFinite)){if(next==='imperial'){setNum('gross',gross*SQFT_PER_M2);setNum('openings',openings*SQFT_PER_M2);setNum('coverage',coverage*COVERAGE_IMPERIAL_PER_METRIC)}else{setNum('gross',gross/SQFT_PER_M2);setNum('openings',openings/SQFT_PER_M2);setNum('coverage',coverage/COVERAGE_IMPERIAL_PER_METRIC)}}currentUnit=next;const imperial=next==='imperial';document.getElementById('areaUnit1').textContent=imperial?'ft²':'m²';document.getElementById('areaUnit2').textContent=imperial?'ft²':'m²';document.getElementById('coverageUnit').textContent=imperial?'ft²/US gal':'m²/L';calculatePaint()}function calculatePaint(){const gross=Number(document.getElementById('gross').value),openings=Number(document.getElementById('openings').value),coats=Number(document.getElementById('coats').value),coverage=Number(document.getElementById('coverage').value),contingency=Number(document.getElementById('contingency').value),out=document.getElementById('result');if(![gross,openings,coats,coverage,contingency].every(Number.isFinite)||gross<0||openings<0||coats<=0||coverage<=0||contingency<0||contingency>100){out.innerHTML='<p><strong>Check the inputs. Areas and the buffer cannot be negative, while coats and coverage must be greater than zero.';return}if(openings>gross){out.innerHTML='<p><strong>Check the areas. The excluded area cannot be larger than the total.';return}const net=Math.max(0,gross-openings),base=net*coats/coverage,planned=base*(1+contingency/100),imperial=currentUnit==='imperial',areaUnit=imperial?'ft²':'m²',volumeUnit=imperial?'US gal':'L';out.innerHTML=`<h3>Estimate: ${fmt(planned)} ${volumeUnit}<p>Paintable area: ${fmt(net)} ${areaUnit} · before buffer: ${fmt(base)} ${volumeUnit} · selected buffer: ${fmt(contingency)}%<p><strong>Compare the result with the package sizes and instructions for the exact paint.`}calculatePaint();
The three numbers you needThe calculation needs the area you will paint, the number of coats and the coverage of the paint—for example 12 m²/L, but only when the manufacturer states that value for the product. Subtract large areas you will not paint, such as doors or large windows.The formula is straightforward: paintable area = total area − excluded area, then required volume = paintable area × coats ÷ coverage. If you want a small buffer, add it separately. The calculator presents it as your choice rather than pretending that 5% or 10% is mandatory for every job.
Worked example: 60 m², two coatsSuppose the walls total 70 m² and large doors and windows account for 10 m². That leaves 60 m² to paint. If the paint is rated at 12 m²/L and you plan two coats, the calculation is 60 × 2 ÷ 12 = 10 L.The base estimate is therefore 10 litres. If you personally choose a 5% buffer, you would plan around 10.5 litres before matching the estimate to available package sizes. The 12 m²/L coverage and 5% buffer are example values, not universal recommendations.
What if the label gives a range?Some manufacturers publish coverage as a range. Bulgarian manufacturer Orgachim, for example, lists 12–15 m²/L and 2 coats for a product in its Spirit Adventure Colours range. That is a product-specific example, not a rule for all interior paints.When you see a range, run two calculations. The higher coverage figure gives the lower quantity; the lower coverage figure gives a more conservative estimate. If the wall is old, rough or highly absorbent, plan cautiously and follow the product instructions for preparation and primer.
Why real consumption can be higherThe arithmetic is a useful starting point, but a wall is not a spreadsheet. Real consumption can increase with a rough or textured substrate, a very absorbent surface, a major colour change, extensive patch repairs or a different application method.Sherwin-Williams notes in its official calculator that the amount needed varies with application method and the type or condition of the surface. Use the manufacturer's coverage figure as the basis of the estimate, but do not treat it as a guarantee for your exact wall.
Turn the estimate into a real purchaseOnce you have an approximate volume, check the package sizes actually sold. If the estimate is 10.5 L and the chosen paint comes in 2.5 L and 5 L cans, compare practical combinations with the price and with whether a small amount of leftover paint would be useful for future touch-ups.This keeps the decision transparent: you can see the calculated volume, the package sizes and the condition of the surface instead of letting a calculator round up according to a hidden rule.
When the calculator is not enoughIf the wall is badly chalking, damp, very uneven or needs specialist preparation, solve the substrate problem first. The calculator can help with paint quantity, but it cannot choose the right primer, repair system or preparation method. Follow the technical data sheet for the exact product and seek specialist advice for more serious substrate problems.The key point: the calculator does the arithmetic. The exact paint and the exact surface determine real consumption.
SourcesOrgachim — Spirit Adventure Colours: product-specific example of a coverage range and number of coats.Sherwin-Williams — Paint Calculator: area, coverage and factors that affect the required amount.Benjamin Moore — Aura Interior Paint: an additional manufacturer example of product-specific coverage data.Checked September 7, 2026. The calculator does not assume one universal coverage figure or a mandatory buffer. This page remains noindex until separate publication approval.
