Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Gallons of exterior paint
9
Net wall area
1,290
sq ft
Exact gallons before rounding
8.60
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter exterior wall perimeter (ft).
- 2Enter average wall height (ft).
- 3Enter doors & windows area (sq ft).
- 4Enter number of coats.
- 5Enter coverage per gallon (sq ft).
- 6Read your gallons of exterior paint on the right — it updates as you type.
- 7Hit Share to keep the scenario or send it to someone.
About this calculator
Exterior house paint follows the same core math as interior paint but with a lower typical coverage rate — often 250-350 sq ft per gallon rather than 350-400 — because textured siding like stucco, wood shakes, or heavily embossed vinyl soaks up more paint per square foot than a smooth interior drywall wall. This calculator takes your home's total exterior wall perimeter and average wall height to compute gross wall area, subtracts window and door openings, then divides by your chosen coverage rate (adjustable for siding texture) and multiplies by coat count, which is typically two coats for full exterior repaints and one for maintenance touch-ups over sound existing paint. Because exterior projects often span multiple stories, gable ends, and trim separate from the main field color, this tool focuses on the main wall field paint and assumes trim, fascia, and soffit paint are calculated and purchased separately since they're usually a different sheen or color. Buying slightly extra exterior paint is generally wiser than interior since exact color-matching outdoors, especially years later for touch-ups, is far more visible than an indoor mismatch.
Worked example
Using the values the calculator loads with:
Inputs
- Exterior wall perimeter: 160 ft
- Average wall height: 9 ft
- Doors & windows area: 150 sq ft
- Number of coats: 2
- Coverage per gallon: 300 sq ft
Results
- Gallons of exterior paint: 9
- Net wall area: 1,290
- Exact gallons before rounding: 8.6
What each field means
Inputs
- Exterior wall perimeter (ft)
- The exterior wall perimeter used in the calculation, measured in ft. Starts at 160 ft so you have a working example on load.
- Average wall height (ft)
- The average wall height used in the calculation, measured in ft. Starts at 9 ft so you have a working example on load. Accepted range: 6–40 ft.
- Doors & windows area (sq ft)
- The doors & windows area used in the calculation, measured in sq ft. Starts at 150 sq ft so you have a working example on load.
- Number of coats
- The number of coats used in the calculation. Starts at 2 so you have a working example on load. Accepted range: 1–3.
- Coverage per gallon (sq ft)
- The coverage per gallon used in the calculation, measured in sq ft. Starts at 300 sq ft so you have a working example on load. Accepted range: 150–400 sq ft.
Results
- Gallons of exterior paint
- Returned as a whole number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Net wall area
- sq ft
- Exact gallons before rounding
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
Why does exterior paint cover less area than interior paint?
Exterior siding textures like stucco, wood shakes, and embossed vinyl or fiber cement have far more actual surface area per square foot of wall than smooth interior drywall, so more paint is absorbed per square foot of footprint.
How many coats does an exterior repaint need?
Two coats is standard for a full color change or a house that hasn't been painted in many years; one coat of maintenance paint can work over sound, similarly-colored existing paint in good condition.
Should trim and siding paint be calculated separately?
Yes, trim, fascia, soffits, and shutters are usually a different color and sheen from the field color, so they should be measured and estimated as a separate, much smaller paint quantity.
Is it worth buying extra exterior paint for future touch-ups?
Yes, exterior paint fades with UV exposure and batch tinting varies slightly, so keeping a labeled leftover gallon from the original project makes future touch-ups blend in far better than a fresh can years later.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
Interior Paint Gallons Calculator
Convert wall square footage into the exact number of gallons and coats you need to buy.
Primer Gallons Calculator
Work out how much primer to buy before you ever open the topcoat can.
Deck Stain Gallons Calculator
Turn deck square footage into gallons of stain, accounting for boards, railings, and stain type.
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Exterior Paint Gallons Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/exterior-paint-gallons-calculator
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/exterior-paint-gallons-calculator" target="_blank" rel="noopener">Exterior Paint Gallons Calculator — RevenueLab</a> (2026).</p>
Source: [Exterior Paint Gallons Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/exterior-paint-gallons-calculator) (2026).