Exterior Paint Calculator
Enter your house dimensions and siding type to get an accurate exterior paint estimate — body, trim, doors, and shutters calculated separately.
1House Dimensions
Measure each wall of your house from outside corner to outside corner. You will enter each wall separately. For a simple rectangular house, you will have 4 walls.
Wall 1 (Front)
Wall 2 (Back)
Wall 3 (Left Side)
Wall 4 (Right Side)
For each gable: width is the wall width, height is from eave to peak. Area = 0.5 × width × height.
2Openings to Subtract
Standard exterior door = 21 sq ft. Standard window = 15 sq ft. Garage door = 160 sq ft (16×10).
3Paint Settings
Coverage rates from Sherwin-Williams exterior paint technical data
Trim typically uses 10-15% of body paint volume
Each standard shutter ≈ 6 sq ft
Your Exterior Paint Estimate
Buying Guide
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Tip: Buy all body paint in the same batch. Color consistency across cans varies slightly — mixing everything from the same batch before painting prevents visible lap lines where cans meet.
How to Use This Calculator
Using this exterior paint calculator ensures you buy the exact amount of paint needed to protect your home. Follow these five steps:
- 1Measure each wall. Use a tape measure to find the length from outside corner to outside corner, and the height from the foundation line up to the eave. Enter each of the four walls into the calculator.
- 2Add gable ends. If your siding extends up into the triangular area under your roof peaks (the gables), check the box to include them. Measure the width of the base of the triangle and the height up to the tip of the peak.
- 3Count all openings. Enter the total number of doors, windows, and garage doors. The calculator automatically subtracts these from your total wall area so you don't overbuy paint.
- 4Select siding type. This is critical. Rough, porous surfaces like heavy stucco or unpainted cedar shingles absorb significantly more paint than smooth fiber cement boards. The calculator adjusts your coverage rate based on Sherwin-Williams exterior technical data.
- 5Decide on trim paint. Trim, fascia boards, and shutters are usually painted a contrasting color and require a different paint formulation (like a semi-gloss) than the main body of the house. Include trim to get a separate gallon estimate just for those details.
The Formula
This exterior paint calculator uses basic geometry and professional coverage rates to determine your material needs. Here is the math in plain English:
Gross Area = Sum of (Wall Width × Wall Height) + (0.5 × Gable Width × Gable Height)
Net Area = Gross Area − (21 × Doors) − (15 × Windows) − (160 × Garage Doors)
Body Gallons = (Net Area × Number of Coats) / Coverage Rate
Trim Gallons = ((Net Area × 0.10) + (Shutters × 6)) × Coats / 400
First, the gross wall area is calculated by multiplying the width and height of all four walls. If you have gable ends, their area is calculated using the standard triangle formula (0.5 times base times height) and added to the total. To get the exact net area to be painted, standard square footage is subtracted for every door, window, and large garage door you counted.
The number of body paint gallons equals that net area multiplied by your coats, divided by the specific coverage rate of your siding type (pulled directly from Sherwin-Williams Duration Exterior technical data sheets). Because measuring every piece of window trim and fascia board is nearly impossible, trim paint gallons are calculated using the industry standard rule of thumb: trim accounts for roughly 10% of the body surface area.
Frequently Asked Questions
As a reference, how many gallons are needed to paint an average 1500 sq ft house?
A standard single-story 1,500 square foot home typically requires about 10 to 12 gallons of body paint and 2 to 3 gallons of trim paint to cover the exterior with two solid coats. If the house is two stories, the footprint is smaller, meaning the wall area is larger, so it will require more paint.
Do I need to prime before painting the exterior, and how does it affect gallon count?
If your existing paint is peeling down to bare wood, or if you are painting brand new, unpainted siding, you absolutely must apply a full coat of exterior primer first. Primer seals the porous surface. If you don't prime bare wood, it will act like a sponge and soak up your expensive topcoat, cutting your paint coverage rate in half.
How do I measure a house with bump-outs or additions?
Do not worry about measuring every tiny jog or bump-out separately. Simply measure the absolute maximum width and depth of the entire house footprint, just as if you were drawing a large rectangle around the entire building. The minor extra wall area created by a bump-out is usually canceled out by the windows located on it.
Should I paint my gutters and downspouts, and are they included in this estimate?
Most modern aluminum gutters have a baked-on factory enamel finish that lasts for decades and does not need to be painted. However, if they are severely faded and you choose to paint them, the 10% trim allowance in this exterior paint calculator provides enough extra paint to cover them.
How long does exterior paint last, and when should I repaint?
A high-quality 100% acrylic exterior paint job should last 7 to 10 years on wood siding and up to 15 years on stucco or fiber cement. You should plan to repaint when you see the color significantly fading or chalking, or immediately if you see the paint beginning to crack, blister, or peel away from the wood.
Can one person paint a house exterior, and how long does it take?
Yes, one determined homeowner can paint an average house, but it is a massive undertaking. Expect to spend a full weekend just pressure washing, scraping peeling paint, and caulking cracks. Applying two coats of paint by hand (brush and roller) to an average house will take a single person roughly 40 to 60 hours of labor.