TryBuildCalcInterior Paint Calculator (Interior & Exterior Paint Quantity)
Estimate paint quantity, coats, wastage, and cost.
Calculate interior paint liters required for walls with coverage and coats. Adjust wall dimensions, coverage, coats, wastage, and price to match your project.
🕒 Last updated: July 14, 2026
Inputs
Section 1: Wall & Surface
ℹ️Use wall length & height if you'd rather let the calculator work out the area, or enter a known wall area directly.
ℹ️Paired with Opening Width below to size a door/window on this wall — leave both blank if there are none. Unit is independent of the wall's own length/height unit.
ℹ️Multiplied by Opening Length to get the deducted area.
ℹ️Adjusts the suggested coverage rate by up to ±30% for how much paint the surface absorbs.
ℹ️Auto-suggested from Paint Type and Surface Condition — still editable.
ℹ️Drives the suggested wastage allowance below — spray loses more to overspray than a roller.
ℹ️Auto-suggested from Application Method and Surface Condition — still editable.
Section 2: Can Size & Cost
ℹ️Check your product's label — common sizes are 1, 4, 10, and 20 liters.
Common can sizes
Recommended paint: 4.20 L (1.11 gal) (1 can)
Net Paintable Area: 24.00 m²
Paint Summary
Gross Wall Area: 24.00 m²
Net Paintable Area: 24.00 m²
Topcoat (before wastage): 4.00 L (1.06 gal)
+ Wastage (5%): 0.20 L (0.05 gal)
Topcoat Required: 4.20 L (1.11 gal)
Cans & Purchase
Recommended Paint: 4.20 L (1.11 gal) total
Topcoat Cans: 1 can
Total Cans: 1 can
Quick Insight
Buy at least 4.20 L (1.11 gal) (1 can) from the same production batch to avoid colour or shade mismatch.
Calculated from wall area, paint coverage, and number of coats.
Assumptions Used
Net area from gross wall area minus openings, coverage-adjusted for paint type and surface condition | Cans rounded up to the next whole can.
Bill of Materials
Main material: 1 cans + recommended tools
+−
Bill of Materials
Main material: 1 cans + recommended tools
Computed items reflect your entered wall dimensions and paint details; consumables below are general recommendations — actual needs vary by product and site.
For Your Job
Topcoat Paint
1 cans
4.2 L total
General Tools & Consumables
Paint roller & tray
Paintbrush (cutting-in)
Masking tape
Drop cloths / floor sheeting
Sandpaper (fine grit)
Approximate results for planning only. Verify with a professional.
Looking for the verification checklist, reference tables, or tips and mistakes?See the complete Paint Calculator.
Interior emulsion estimate
This page defaults to an 8 m x 3 m wall (24 m²) with Interior Emulsion at its standard 12 m²/L coverage — that's 4 liters raw for 2 coats, or 4.2 liters after 5% wastage, rounding up to 1 can of 10 L.
12 m²/L is this calculator's baseline coverage for Interior Emulsion on a standard (smooth, previously-painted) surface — a rougher new-plaster surface would drop that rate and raise wastage together, since porous surfaces absorb more paint on the first coat.
- Wall: 8 m x 3 m (24 m²).
- Paint: interior emulsion, 12 m²/L.
- Cans: 1 (10 L can).
How paint calculation works
Step 1 — Net paintable area
Openings (doors, windows, fixed units) are optional — leave blank to paint the full gross area.
Step 2 — Topcoat requirement
Coverage is auto-suggested from Paint Type and Surface Condition, and always overridable.
Step 3 — Primer requirement (optional add-on)
Calculated separately from the topcoat and added alongside it — not chosen instead of it — since primer and topcoat are different products bought in their own cans.
Step 4 — Add wastage allowance
Wastage is auto-suggested from Application Method and Surface Condition (5% roller, 7% brush, 12% spray, bumped further for a rough surface or multiple walls), and covers roller/brush losses, spillage, and tray residue.
Step 5 — Convert to cans
Topcoat and primer cans are rounded up separately, since they're different products.
Real-World Paint Calculation Example
This example uses the active inputs above and follows the same steps from the formula section.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Wall size | 8 m x 3 m | Determines whether gross area comes from length x height or a direct entry |
| Paint Type / Surface Condition | Interior Emulsion (~12 m²/l) / Standard new putty/plaster finish | Sets the auto-suggested coverage rate below |
| Coverage x Coats | 12 m²/liter x 2 | Converts net area into raw topcoat liters |
| Application Method / Wastage | Roller / 5% | Adds allowance for roller/brush loss and spillage before rounding to cans |
| Primer | Off | Adds a separate primer line alongside the topcoat when switched on |
| Can size / Cost estimation | 10 L / Off | Rounds final liters to whole cans, and prices them when enabled |
Step 1 — Net Paintable Area
| Calculation | Formula / Substitution | Result |
|---|---|---|
| Gross area | 8 m x 3 m | 24 m² |
| Net paintable area | No openings deducted | 24 m² |
Step 2 — Topcoat Requirement
| Calculation | Formula / Substitution | Result |
|---|---|---|
| Raw topcoat | (24 ÷ 12) x 2 coats | 4 liters |
| Final topcoat (incl. wastage) | 4 x (1 + 5%) | 4.2 liters |
Step 3 — Cans
| Calculation | Formula / Substitution | Result |
|---|---|---|
| Topcoat cans | ROUND UP(4.2 ÷ 10 L) | 1 can |
| Total cans | Topcoat cans | 1 can |
Therefore, for a 24 m² wall with 2 coats, you need 4.2 liters of paint, or 1 can.
Actual paint consumption may vary depending on surface condition, paint quality, application method, and wall preparation. For a full room, switch on Multiple Walls and add each wall as its own row.
This page keeps things focused on the calculation above. For the full construction guide — verification checklist, reference tables, usage steps, tips, common mistakes, and limitations.See the complete Paint Calculator.
Related Calculators
Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.