Fields marked * are required.
sq ft / gallon
Typical: smooth ~ 350-400, rough ~ 200-300.
Adjusts a factor for coverage realism.
Walls / Siding Areas
| # | Count | Width | Height | Area |
|---|
Width and height in selected units. Area auto-computes.
Gable Triangles (optional)
| # | Count | Base | Height | Area |
|---|
Area = 0.5 × base × height.
Trim / Soffits (optional)
ft
ft
Paint one or more faces.
Openings to Subtract (doors, windows)
| # | Count | Width | Height | Area |
|---|
Results
Net paint area: 0 sq ft
Effective coats: 0
Adjusted coverage: 0 sq ft / gal
Paint required: 0 gallons
Rounded purchase: 0 gallons
Factors reflect surface absorption and profile. Always confirm manufacturer coverage.
Example Data
Click to load into the form.
| Scenario | Walls | Openings | Coats | Coverage |
|---|---|---|---|---|
| Small ranch | 4 × (24×9) | 7 windows 3×4, 2 doors 3×7 | 2 | 350 sq ft/gal |
| Gables plus trim | 2 × (30×10), 2 × (20×10) | 8 windows 3×4, 2 doors 3×7 | 2 + primer | 300 sq ft/gal |
Formulas Used
- Wall area:
A_wall = sum(count × width × height) - Gable area:
A_gable = sum(count × 0.5 × base × height) - Trim area:
A_trim = length × width × faces - Openings:
A_open = sum(count × width × height) - Net area:
A_net = A_wall + A_gable + A_trim − A_open - Effective coats:
N_eff = coats + primer - Surface factor
kby surface type (smooth=1.00, rough=1.25, stucco=1.35, wood=1.15) - Adjusted coverage:
C_adj = coverage ÷ k - Base volume:
V = (A_net × N_eff) ÷ C_adj - Waste-adjusted:
V_w = V × (1 + waste/100) - Units: Imperial uses sq ft/gal; Metric uses m²/L. Conversions:
1 gal = 3.785 L,1 m = 3.28084 ft.
How to Use
- Select units and enter coats, coverage, and waste percentage.
- Add walls with width and height. Use counts for repeats.
- Add gables if applicable. Triangles use base and height.
- Enter linear trim length and width; set faces painted.
- Add openings to subtract. Doors and windows reduce area.
- Choose primer if required and a rounding preference.
- Click Calculate. Review net area and volumes.
- Export your scenario using Download CSV or Download PDF.
How Do You Calculate Square Footage for Exterior Painting?
Use a simple measure‑and‑subtract workflow to get a reliable paint area before applying coats and waste factors. The same logic works in feet or meters.
- Measure each wall: record width and height. Area per wall is
width × height. - Include gables: treat triangular sections as
0.5 × base × heightadded to the wall below. - Add trim if painting separately: linear trim area is
length × trim width × faces(faces = 1 or 2). - Subtract openings: for doors and windows use
width × heightand subtract from the total. - Sum all components:
Anet = ΣAwalls + ΣAgables + Atrim − ΣAopenings. - Apply coats: multiply by the number of finish coats; add a primer coat if required.
- Account for texture and waste: rough surfaces cover less; add 5–15% waste for losses and touch‑ups.
Quick Example (Imperial)
Ranch house with four walls 24×9 ft, seven windows 3×4 ft, two doors 3×7 ft, and one gable 20×6 ft. Net area:
- Walls:
4 × (24 × 9) = 864 sq ft - Gable:
0.5 × 20 × 6 = 60 sq ft - Openings:
7 × (3 × 4) + 2 × (3 × 7) = 84 + 42 = 126 sq ft - Net area:
864 + 60 − 126 = 798 sq ft
For two coats and 7% waste, paint volume is V = (798 × 2 ÷ coverage) × 1.07. Choose coverage from the product datasheet.
Coverage Reference by Surface
| Surface / Condition | Coverage (sq ft/gal) | Coverage (m²/L) | Notes |
|---|---|---|---|
| Smooth, previously painted | 350–400 | 8.6–9.8 | Best case with quality topcoat and roller. |
| Rough or textured siding | 200–300 | 4.9–7.4 | Higher profile reduces spread rate. |
| Stucco / masonry | 150–250 | 3.7–6.1 | Porous; consider primer or block‑filler. |
| Bare wood (primer) | 250–350 | 6.1–8.6 | First coat often absorbs more. |
Convert ft²/gal to m²/L using 1 ft² = 0.092903 m² and 1 gal = 3.785 L.
Common Openings Size Guide
| Opening Type | Width × Height (ft) | Area (sq ft) |
|---|---|---|
| Window (small) | 2.5 × 4 | 10.0 |
| Window (standard) | 3 × 4 | 12.0 |
| Door (single) | 3 × 7 | 21.0 |
| Patio slider | 6 × 7 | 42.0 |
| Garage (single) | 8 × 7 | 56.0 |
| Garage (double) | 16 × 7 | 112.0 |
Subtract openings from wall area unless they will be painted.
Texture Factor (k) Reference
| Surface Type | Factor k | Adjusted Coverage Example | Comment |
|---|---|---|---|
| Smooth / previously painted | 1.00 | 350 ÷ 1.00 = 350 ft²/gal | Benchmark case. |
| Bare wood | 1.15 | 350 ÷ 1.15 ≈ 304 ft²/gal | More absorption, lower spread rate. |
| Rough / textured | 1.25 | 350 ÷ 1.25 = 280 ft²/gal | Deeper profile increases usage. |
| Stucco / masonry | 1.35 | 350 ÷ 1.35 ≈ 259 ft²/gal | Often needs block‑filler or primer first. |
The calculator applies k automatically via “Surface Type.” Coverage is divided by k to reflect roughness and porosity.
Cost Estimator
Example: $, €, £, PKR
sq ft/hr/coat (editable)
Material Volumes
Finish volume (total): 0.00 gallons
Wall: 0.00 · Trim: 0.00
Primer volume: 0.00 gallons
Material Cost
Finish paint (wall+trim): 0.00
Wall: 0.00 · Trim: 0.00
Primer: 0.00
Sundries: 0.00
Materials subtotal: 0.00
Labor
Estimated hours: 0.0
Labor cost: 0.00
Hours = net area × coats ÷ productivity.
Total
Pre-tax total: 0.00
Tax: 0.00
Grand total: 0.00
Unit costs: —