Paint Coverage Calculator

This calculator estimates how much paint you need by computing paintable surface area, accounting for doors and windows, the number of coats, manufacturer coverage per gallon, waste allowance, and chosen can sizes. Use the defaults as a starting point and adjust coverage and waste based on surface texture and paint type.

Results include net paintable area, gallons required (before rounding), recommended number of cans based on your selected can size, total gallons to purchase, and an estimated cost. The methodology follows standard surface-area calculations used by building science and extension services.

Updated Nov 18, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record baba6b7c2f6e • Reviewed by Fidamen Standards Committee

Inputs

Room length (ft)

Min 0.5 · Max 200

Room width (ft)

Min 0.5 · Max 200

Wall height (ft)

Min 0.5 · Max 50

Include ceiling? (1 = yes, 0 = no)

Min 0 · Max 1

Number of doors

Min 0 · Max 50

Average door area (sq ft)

Min 1 · Max 200

Number of windows

Min 0 · Max 50

Average window area (sq ft)

Min 1 · Max 500

Number of coats

Min 1 · Max 10

Manufacturer coverage (sq ft per gallon)

Min 50 · Max 2000

Allow for waste/overlap (%)

Min 0 · Max 100

Can size to purchase (gallons)

Min 0.1 · Max 20

Price per gallon (USD)

Min 0 · Max 1000

Results

Updates as you type

Net paintable area (sq ft)

301

Total paint area for coats (sq ft)

602

Gallons required (before rounding)

1.9111

Recommended cans (count)

—

Gallons to purchase

—

Estimated paint cost

—

Output	Value	Unit
Net paintable area (sq ft)	301	sq ft
Total paint area for coats (sq ft)	602	sq ft
Gallons required (before rounding)	1.9111	gallons
Recommended cans (count)	—	—
Gallons to purchase	—	gallons
Estimated paint cost	—	USD

Primary result301

Visualization

Points

Methodology

Measure room dimensions (length, width, height). Wall area = 2 × (length + width) × height. Add ceiling area if painting the ceiling. Subtract the area of doors and windows to get net paintable area.

Multiply net area by number of coats to get total paint area. Divide total paint area by effective coverage per gallon. Effective coverage = manufacturer coverage × (1 − waste allowance). Round up to whole cans when purchasing.

Defaults (coverage and waste) reflect typical professional guidance; actual coverage varies with paint formulation, primer use, surface porosity and texture. For technical unit definitions and measurement standards see NIST and extension resources listed below.

F.A.Q.

How accurate is the coverage estimate?

This tool uses manufacturer coverage and a user-specified waste allowance to estimate paint needed. Coverage varies by porosity, texture, color change, primer use, and application method. For final ordering add a modest buffer (commonly 5–15%).

What coverage per gallon should I use?

Start with the manufacturer's published coverage (sq ft per gallon). Typical values for interior paints range from about 300–400 sq ft per gallon. Use higher values for smooth, primed surfaces and lower for rough or unprimed surfaces.

Should I count primer separately?

If you will apply a dedicated primer, treat it as a separate product: calculate primer gallons using the same area but the primer's coverage rate. Some coatings combine primer and paint; follow manufacturer guidance.

How do I measure odd-shaped rooms or cabinets?

Break complex shapes into rectangles and circles, calculate each area, then sum them. Subtract fixed openings (doors/windows). For cabinetry or furniture, measure surface area of each face and add edges as needed.

How should I dispose of leftover paint?

Follow local hazardous-waste guidance. The U.S. EPA provides recommendations for household hazardous waste and paint disposal—check local government programs for recycling or drop-off options.

What safety precautions should I follow?

Use adequate ventilation, follow product safety data sheets (SDS), and wear appropriate respirators, gloves and eye protection for solvent- or aerosol-based paints. Consult OSHA/NIOSH guidance for workplace safety when using industrial coatings.

Sources & citations

NIST — SI units & measurement resources — https://www.nist.gov/pml/weights-and-measures/metric-si-units
U.S. EPA — Household hazardous waste and paint disposal guidance — https://www.epa.gov/hw/household-hazardous-waste
Cooperative Extension resources — measurement and painting guidance — https://extension.org
ACI — American Concrete Institute Standards — https://www.concrete.org/publications/typesofpublications/standards(codesandspecs).aspx
ACI 211.1-91 — Standard Practice for Selecting Proportions for Concrete — https://www.concrete.org/
ASTM International — Construction Standards — https://www.astm.org/

Further resources

Related tools

Versioning & Change Control

Audit record (versions, QA runs, reviewer sign-off, and evidence).

Record ID: baba6b7c2f6e

What changed (latest)

v1.0.0 • 2025-11-18 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Public QA status

PASS — golden 25 + edge 120

Last run: 2026-01-23 • Run: golden-edge-2026-01-23

Engine

v1.0.0

Data

Baseline (no external datasets)

Content

v1.0.0

Governance

Last updated: Nov 18, 2025

Reviewed by: Fidamen Standards Committee (Review board)

Credentials: Internal QA

Risk level: low

Reviewer profile (entity)

Fidamen Standards Committee

Review board

Internal QA

Entity ID: https://fidamen.com/reviewers/fidamen-standards-committee#person

Semantic versioning

MAJOR: Calculation outputs can change for the same inputs (formula, rounding policy, assumptions).
MINOR: New features or fields that do not change existing outputs for the same inputs.
PATCH: Bug fixes, copy edits, or accessibility changes that do not change intended outputs except for previously incorrect cases.

Review protocol

Verify formulas and unit definitions against primary standards or datasets.
Run golden-case regression suite and edge-case suite.
Record reviewer sign-off with credentials and scope.
Document assumptions, limitations, and jurisdiction applicability.

Assumptions & limitations

Uses exact unit definitions from the Fidamen conversion library.
Internal calculations use double precision; display rounding follows the unit's configured decimal places.
Not a substitute for calibrated instruments in regulated contexts.
Jurisdiction-specific rules may require official guidance.

Change log

v1.0.0 • 2025-11-18 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Areas: engine, content, ui • Reviewer: Fidamen Standards Committee • Entry ID: 383b9ed74d3a