Paint Qty Calculator
Estimators and purchase-order writers often abbreviate 'paint quantity' as 'paint qty' on takeoff sheets. This paint qty calculator returns the exact gallons and liters needed for a painting job, then rounds up to the container size you actually buy: quart, 1-gallon can, or 5-gallon bucket.
Paint Qty Formula
Paint qty in gallons is just:
Paint Qty = (Net Wall Area x Coats) / Coverage Rate
Where net wall area is gross wall area minus 21 sq ft per door and 15 sq ft per window. Coverage rate depends on surface:
| Surface | Coverage per Gallon |
|---|---|
| Interior smooth drywall | 350 sq ft |
| Exterior primed siding | 300 sq ft |
| Textured wall | 250 sq ft |
| Rough masonry or stucco | 200 sq ft |
| Ceiling (flat paint) | 400 sq ft |
Paint Qty Example
A 500 sq ft wall area, 2 coats, interior smooth drywall:
- Net area (no openings): 500 sq ft
- Total coverage: 500 x 2 = 1,000 sq ft
- Paint qty: 1,000 / 350 = 2.86 gallons
Round up to 3 gallons (three 1-gallon cans) or 1 five-gallon bucket with 2 gallons left over.
When Contractors Use Paint Qty
The term "paint qty" shows up on:
- Takeoff sheets for commercial estimators pricing multi-room jobs
- Purchase orders where the PO system has a shortened quantity field
- Spreadsheet line items where column widths force abbreviation
- Mobile paint-ordering apps that echo contractor shorthand
The underlying math is identical to any paint calculator. This tool just exposes it under the specific phrasing contractors search for.
Container Sizes
Paint retail follows a 3-tier container scheme in the US:
- Quart (0.25 gal) covers ~88 sq ft. Use for trim, touch-ups, or accent walls under 40 sq ft.
- 1-gallon can covers 350 sq ft on smooth interior drywall. The default residential size.
- 5-gallon bucket covers 1,750 sq ft. Saves 20-30% per gallon vs 1-gallon cans. Buy buckets whenever paint qty is 3+ gallons.
Coverage Rate Details
Published coverage rates are the best case. In practice, plan on:
- New drywall: 15-20% more paint than the label says. Bare drywall is thirstier than previously-painted surfaces.
- Color change: 2 coats always; add a tinted primer if going dark-to-light.
- Wooden exterior (lap siding): 275-300 sq ft/gal. Cedar and redwood soak up more than pine.
- Masonry block (split-face): 150 sq ft/gal. Order double what a smooth-wall calculation predicts.
- Cement board siding (HardiePlank): 300-350 sq ft/gal if factory-primed, 200-250 if raw.
Professional Takeoff Workflow
A commercial estimator generating a paint qty line item:
- Measure wall perimeter x ceiling height from plans
- Deduct openings (doors, windows, large vents)
- Multiply by number of coats specified in finish schedule
- Divide by coverage rate for the specified paint system
- Round up to the nearest gallon
- Add 5-10% waste for site-specific conditions
The calculator above automates steps 1-5 and lets you set waste at step 6 using the container rounding.