How to Calculate Paint for a Contracting Job
Accurate paint estimation is critical for profitable contracting. Over-ordering wastes materials cost and ties up capital. Under-ordering causes project delays and colour inconsistency from different dye lots. Professional contractors use a systematic room-by-room approach to calculate total paint quantities for every project.
The standard formula for wall paint is: total wall area minus door and window deductions, divided by coverage rate per gallon, multiplied by number of coats. A professional crew typically uses a coverage rate of 350 to 380 square feet per gallon for interior smooth walls — slightly below the label rate to account for cutting in, roller waste, and touch-ups.
Add 10% waste allowance for standard projects and 15% for cut-up rooms with many windows, doors, and obstacles. Add 20% for new construction where walls may be more absorbent and extra touch-up is required after other trades finish.
Contractor Paint Estimating — Reference Table
| Project Type | Coverage Rate | Waste Factor | Coats |
|---|---|---|---|
| Interior repaint | 370 sq ft/gal | 10% | 2 |
| New construction interior | 350 sq ft/gal | 15% | 2 |
| Exterior repaint | 300 sq ft/gal | 10% | 2 |
| New exterior (bare) | 250 sq ft/gal | 15% | 2 |
| Ceiling repaint | 380 sq ft/gal | 10% | 1–2 |
| Trim and doors | 200 sq ft/gal | 15% | 2 |
How to Price a Painting Job
Professional painters price jobs using one of three methods: price per square foot, hourly rate, or project-based pricing. Price per square foot is the most common — $2 to $6 per square foot for interior painting depending on your market, complexity, and finish level. Exterior painting runs $1.50 to $4.50 per square foot.
A typical interior repaint job breakdown: materials are 15 to 25% of total job cost, labour is 70 to 80%, and overhead and profit is 10 to 15%. Beginners often underprice labour. Always calculate your actual hourly rate — include travel time, prep time, cleanup time, and equipment maintenance — before pricing any job.
For commercial painting projects, add separate line items for surface preparation, primer, number of coats, and any specialty coatings. Commercial clients and property managers expect detailed itemised quotes, not lump sum pricing.
Best Paint Brands for Contractors
Sherwin-Williams ProClassic and Duration are the most widely used professional interior paints — available through Sherwin-Williams contractor accounts at significant discounts from retail price. Benjamin Moore Regal Select and Aura are the premium choices that clients recognise by name and are willing to pay a premium for.
For exterior commercial projects, Sherwin-Williams Emerald Exterior and Duration Exterior provide the best durability and warranty coverage. Many commercial contracts specify paint brands — always confirm with the client before purchasing materials.
Contractor Painting Tips
Open a contractor account. Sherwin-Williams, Benjamin Moore, and PPG all offer contractor accounts with 30 to 40% off retail pricing. The savings on a full year of jobs easily justify the paperwork.
Box your paint for large jobs. Pour all cans of the same colour into a large bucket and mix before starting. This eliminates colour variation between cans from different batches.
Use a paint tracker spreadsheet. Track paint quantities used per room on every job. Over time this builds your own real-world coverage database for your specific methods and markets.
Always do a site visit before quoting. Never quote a painting job from photos or measurements alone. Surface condition, accessibility, and prep requirements can double or triple material and labour costs.
Related Paint Calculators
- Whole House Paint Calculator →
- Paint Cost Calculator →
- Paint Coverage Calculator →
- Exterior Paint Calculator →
- Primer Calculator →
- Free Paint Calculator →
Frequently Asked Questions
How do contractors calculate how much paint they need?
Measure total wall area, subtract doors and windows, divide by coverage rate (350 to 380 sq ft per gallon for interior), multiply by number of coats, then add 10 to 15% waste. Use our calculator above for each room and it totals automatically.
How much do painters charge per square foot?
Interior painting costs $2 to $6 per sq ft including labour and materials. Exterior painting costs $1.50 to $4.50 per sq ft. Rates vary by market, complexity, and finish quality.
What paint do professional painters use?
Sherwin-Williams Duration and ProClassic, Benjamin Moore Regal Select and Aura are the most used professional paints. Contractors buy through accounts at 30 to 40% off retail pricing.
How much paint do I need for a 2000 sq ft house?
A 2,000 sq ft home interior needs 18 to 22 gallons for two coats on all walls. Add 4 to 6 gallons for ceilings and 2 to 3 gallons for trim. Buy in 5-gallon buckets for bulk savings.
How do you bid a painting job?
Calculate materials (15 to 25% of job total), estimate labour hours at your hourly rate (70 to 80%), add overhead and profit (10 to 15%). Always do a site visit before quoting. Never bid from photos alone.
What is the average paint job profit margin?
Professional painting companies target 15 to 25% net profit margin. New contractors often underprice labour. Always calculate your true hourly cost including travel, prep, and cleanup before pricing any job.