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PAINTING

Paint Calculator.

Estimate wall paint from the actual room perimeter and wall height, then remove doors and windows and apply the number of coats. Advanced mode can add ceiling paint, primer, contingency and supplier container-size purchasing.

Compare litres with US gallons and coverage in m²/L or ft²/gal; use the product label for the surface-specific rate.

IMPERIAL + METRIC · LIVE CALCULATION
PAINT CALCULATOR — CALCULATE
Calculator mode
Calculated result: 3 gallons
YOUR RESULT3 gallons

388 ft² of wall surface after openings, across 2 coats.

BASE BREAKDOWN
Wall area448 ft²
Paintable area388 ft²
Unrounded quantity2.22
Buy3 gallons
Calculated in your browser
HOW IT WORKS

Formula and calculation method.

Paint = ((2 × (length + width) × height − openings) × coats) ÷ coverage

The four walls are represented by room perimeter multiplied by wall height. Openings are removed before multiplying by coats. Coverage converts coated surface area into gallons or litres. Advanced mode can add the rectangular ceiling, primer coats, contingency and whole-container ordering.

WORKED EXAMPLES

See the material estimate in context.

Bedroom repaint

16 ft × 12 ft room, 8 ft walls, 60 ft² openings, 2 coats, 350 ft²/gal

Result: About 2.22 gal for the base wall calculation before Advanced contingency and container rounding.

A second coat doubles coated wall area, while doors and windows reduce wall area first.

Metric room

4.8 m × 3.6 m, 2.5 m walls, 5 m² openings, 2 coats, 10 m²/L

Result: About 7.9 litres for the base wall calculation before Advanced options.

Use the exact product-label coverage because porous or textured walls can consume more.

USE IT CAREFULLY

Assumptions and common mistakes.

Assumptions

  • The room is rectangular with four full-height walls.
  • Openings entered will not be painted.
  • Finish coats use the entered coverage rate.
  • Coverage is a practical estimate, not a guarantee.

Mistakes to avoid

  • Forgetting the second coat.
  • Using floor area instead of wall perimeter and height.
  • Subtracting doors or windows that will actually be painted.
  • Using ideal label coverage on porous unprimed surfaces without allowance.
EDGE CASES

Handle unusual projects explicitly.

Feature walls

Calculate the feature wall separately when it uses a different colour, product or number of coats.

Ceilings

Basic mode covers walls. Advanced mode can add the rectangular room ceiling to the coated area.

Very large openings

If openings approach or exceed calculated wall area, recheck the measurements rather than assuming a negative paint requirement.

LIMITATIONS

What the estimate leaves out.

Trim, doors, spray loss, surface absorption, unusual geometry and exact manufacturer pack combinations may still require separate planning. Advanced primer is an estimate; confirm primer and finish coverage plus available container sizes on the product labels.

FAQ

Material planning questions.

How many coats should I enter?

Use the number you expect to apply. Two coats are common, but colour change, substrate and product instructions can require more or less.

Can the calculator include a ceiling?

Yes. Basic mode calculates walls; Advanced mode can add the rectangular ceiling area.

Can it estimate primer?

Yes. Advanced mode can estimate primer coats, but confirm the primer product coverage before purchasing.

Should I round paint up?

Yes. Advanced mode can use the container size you enter to produce a whole-container purchase quantity.

PRACTICAL GUIDE

Paint Calculator guide

Use this calculator to turn a rectangular room into a paint quantity from the surfaces that will actually be coated. The core wall estimate starts with room perimeter × wall height, subtracts entered door and window area, multiplies by the number of coats, and divides by the coverage rate. Advanced options can account for ceiling paint, primer, contingency, and the container sizes you can actually buy.

The coverage number is deliberately an input rather than a universal FigureNest constant. Paint labels and technical data sheets state coverage for a particular product and conditions; porous, textured, repaired, unsealed, or strongly contrasting surfaces can use materially more paint. Use the manufacturer’s figure for the product and substrate whenever it is available.

FORMULA AND VARIABLES

How the calculation works.

FormulaWall paint = ((2 × (length + width) × height − openings) × coats) ÷ coverage
  • length and width = room dimensions used to find the wall perimeter
  • height = wall height from the painted lower edge to the painted upper edge
  • openings = total door and window area that will not be painted
  • coats = complete finish coats planned for those walls
  • coverage = area one unit of paint covers for one coat, using a compatible area/unit basis
WORKED EXAMPLE

Follow the numbers in context.

16 ft × 12 ft bedroom

The perimeter is 2 × (16 + 12) = 56 ft. At 8 ft high, gross wall area is 448 ft². Subtract 60 ft² of doors and windows to leave 388 ft². Two coats require 776 ft² of coverage. At 350 ft² per gallon, the mathematical requirement is 2.22 gallons before any chosen contingency or container-size rounding.

4 m × 3 m room

A 4 m by 3 m room has a 14 m perimeter. At 2.5 m high, gross wall area is 35 m². After 4 m² of openings, 31 m² remains. Two coats require 62 m² of coverage; at 10 m²/L, that is 6.2 L before contingency and whole-container purchasing.

WHAT THE RESULT TELLS YOU

Use the number for the question this tool answers.

Read the unrounded paint quantity as the modeled liquid requirement for the entered geometry, coats, and coverage rate. It is useful for comparing scenarios because each assumption is visible.

Treat contingency as a planning choice, not a substitute for an accurate coverage rate. Extra paint may be useful for roller loss, touch-ups, repairs, or future matching, but the appropriate amount depends on the job.

If the result changes sharply when you adjust coverage, verify the product data and substrate condition before buying; coverage is often the most uncertain input.

Keep a note of product, color, sheen, batch information, entered coverage, and purchased quantity so later touch-up decisions are based on the same assumptions.

More detail: inputs, assumptions, mistakes and edge cases
HOW TO USE IT

Build a dependable estimate.

  1. Measure room length, width, and wall height; split rooms with materially different heights or shapes into separate estimates.
  2. Measure the doors and windows you genuinely will not paint and enter their combined area. Do not subtract trim that will receive the same coating.
  3. Choose the number of finish coats for the actual repainting job and enter the product’s stated coverage rate on the same area-per-volume basis used by the calculator.
  4. Use advanced options only for items that belong in your scope: ceiling, primer, contingency, and available container sizes.
  5. Compare the calculated liquid quantity with sold can sizes and round purchasing upward where partial containers cannot be bought.
UNITS AND INPUTS

Keep measurements compatible.

Keep room dimensions, opening area, and coverage on compatible imperial or metric bases. A coverage figure in square metres per litre cannot be used as though it were square feet per gallon.

Coverage is per coat. The calculator multiplies net paintable area by the entered coat count before dividing by coverage.

A liquid result such as 2.22 gallons is a mathematical quantity, not automatically a purchasable package. Container-size ordering is a separate step.

ASSUMPTIONS AND LIMITATIONS

Know what the result includes.

Assumptions

  • The room is represented by a rectangle with one wall height for the core wall calculation.
  • Entered opening area is not painted and is subtracted once from gross wall area.
  • The same entered coverage rate applies across the modeled finish coats.
  • The entered number of coats represents complete coverage passes over the net area.

Limitations

  • The calculator cannot predict real spread rate from substrate porosity, texture, application method, color change, thinning, overspray, or painter technique.
  • It does not decide whether primer is required, whether one product can coat a particular substrate, or how many coats a manufacturer requires.
  • Irregular rooms, stairwells, vaulted surfaces, cabinetry, trim, radiators, feature walls, and partially painted surfaces may need separate measured areas.
  • A quantity estimate does not replace the paint manufacturer’s preparation, coverage, drying, recoating, safety, and application instructions.
COMMON MISTAKES

Avoid preventable errors.

  • Using floor area as wall area. Wall paint starts from perimeter × wall height, not room length × width.
  • Forgetting that two coats require roughly twice the paintable coverage of one coat at the same spread rate.
  • Treating a typical online coverage number as more authoritative than the label or technical sheet for the paint being purchased.
  • Subtracting doors and windows that will be painted with the same product, or subtracting the same opening twice.
  • Rounding the liquid requirement down to the nearest can size and then running short during the final coat.
EDGE CASES

Check unusual inputs carefully.

If a room has different wall heights, calculate those wall sections separately rather than averaging a height that hides the geometry.

A very porous new surface may need primer or a different effective coverage rate; model the finish paint only after deciding the preparation system.

A dramatic color change can alter the practical number of coats even when the room geometry is unchanged.

When only one wall is being painted, calculate that wall as its own rectangular surface rather than entering a whole-room perimeter.

FAQ

Questions about this calculation.

Should I use the coverage printed on the paint can?

Yes, when it applies to your product and surface. Manufacturer coverage is more relevant than a generic internet average, and actual spread can still vary with substrate and application.

Why does the calculator multiply by the number of coats?

Coverage is normally stated for one coat over a given area. Painting the same net area twice requires two area-passes.

Should I subtract doors and windows?

Subtract only surfaces that will not receive this paint. If a door, panel, or other surface is being coated with the same product, keep its area in the relevant estimate.

Does the result include primer?

Primer is a separate coating with its own coverage and suitability. Use the advanced primer option where applicable and verify the selected primer’s product data.

Why is the calculated amount not the same as the cans I should buy?

Paint is sold in fixed container sizes. The formula can return a fractional liquid quantity, while purchasing must be rounded to available packages.

Can this tell me whether I need one, two, or three coats?

No. That depends on the paint system, existing color and condition, substrate, preparation, and manufacturer instructions. Enter the coat count appropriate to the job.

RELATED TOOLS AND GUIDES

Continue the calculation.

Square Footage CalculatorMeasure a separate rectangular wall or ceiling area.Drywall CalculatorEstimate sheet quantities before finishing and painting a room.Construction materials estimatingSeparate measured geometry, allowances, and purchasable quantities.
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