Room and exterior paint

Exterior house paint calculator

Sum rectangular elevations and gable triangles, subtract openings, and estimate siding and trim products separately.

Your project measurements

A worked example is prefilled. Replace its values with your measurements and current product data.

Sum each exterior wall elevation before gables and openings.

Enter zero when there are no gables.

Measure from the wall top to the gable peak; enter zero if none.

Whole number of equal triangular gables; enter zero if none.

Sum doors and windows across the measured wall faces.

Use the current product rate for the siding surface and method.

Whole number from the product instructions.

Measure trim faces separately; enter zero if none.

Required when trim area is greater than zero.

Required when trim area is greater than zero.

Optional allowance for your project. This is not a product recommendation.

Your estimate

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Project notes

Understand this estimate

Exterior siding area combines measured rectangular elevations and optional triangular gables, then subtracts unpainted openings. Trim is kept as a separate product estimate.

How to use the calculator

  1. Sum rectangular wall elevations

    Add each wall’s rectangular area before subtracting doors, windows or gables.

    Inputs Total rectangular wall area

  2. Add gables and subtract openings

    Enter matching triangle dimensions and count, or leave all gable values at zero. Deduct unpainted openings once.

    Inputs Gable base width · Gable rise · Matching gable count · Unpainted openings

  3. Estimate siding and optional trim separately

    Use product-specific coverage and coats. When trim area is positive, enter its own coverage and coat count.

    Inputs Siding product coverage · Siding coats · Separately measured trim area · Trim product coverage · Trim coats · Extra allowance

Formula and variables

Gross siding area = rectangular wall area + (gable base × gable rise ÷ 2 × gable count). Net siding area = gross siding area − openings. Siding and trim quantities use their own area, coverage and coat count.

b × h ÷ 2 × nGable area
Triangle base, rise and matching gable count.ft²
W + G − ONet siding area
Rectangular walls plus gables minus openings.ft²
A ÷ C × NProduct quantity
Calculated independently for siding and trim.US gal

What the result means

Result interpretation

Net siding area and siding estimate exclude trim. Trim area and its estimate appear separately when supplied. Roof planes, soffits and profile multipliers are not included.

Limits and assumptions

Exclude roof planes and soffits. Use measured or source-supported siding area for profiled surfaces; the calculator does not add an invented roughness factor or determine paint suitability.

Worked example

Two elevations, one gable and measured trim

Assumptions
  • Rectangular wall area totals 400 ft².
  • One 40 × 5 ft triangular gable and 60 ft² of openings.
  • Trim is measured separately at 100 ft².
Calculation
  1. 400 + 40 × 5 ÷ 2 − 60 = 440 ft² siding.
  2. 440 ÷ 400 × 2 = 2.2 gal siding.
  3. 100 ÷ 300 × 2 = 0.6667 gal trim.
Expected result
Net siding area440 ft²
Siding paint estimate2.2 US gal
Measured trim area100 ft²
Trim paint estimate0.6667 US gal

Common questions

Are roof, soffit and fascia areas included?
No. Measure any additional paintable surfaces separately; the current tool estimates walls, gables and measured trim.
Why separate trim coverage?
Trim may use a different product or spread rate, so its quantity is calculated on its own inputs.

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