Title: Paint calculator | Cercha
Description: Estimate US gallons from surface area, exclusions, coats, and product coverage. Add waste and check the whole-gallon quantity.
Canonical: https://cercha.pages.dev/tools/paint-calculator/
# Paint calculator
Construction calculators
Check paint quantity for one product and color using measured surfaces and the selected coverage.
You need paint quantities before a room starts or a check on the painter’s material list. Enter measured surface area, the area excluded from that paint, coat count, and product coverage per coat. The calculator applies your waste allowance and returns estimated US gallons and a whole-gallon option.
## Measure surfaces by product and color
Measure each wall face’s covered length and height, then add its area to the matching paint group. Measure ceilings separately. Keep trim, another color, or a different product in its own calculation instead of folding everything into one purchase count.
Enter gross surface area and deduct the measured area that will not receive this paint. If your area is already net, leave the exclusion at zero. This tool has no room-dimension inputs and does not convert floor area into wall area.
## Use coverage for the selected paint
The [Sherwin-Williams Painter Skills Program](https://images.sherwin-williams.com/content_images/sw-pdf-painter-skills-training-class-presentation-presenter-notes.pdf) calculates net paintable area and divides by coverage to estimate gallons for a coat. This tool multiplies net area by the coat count, adds your allowance, and divides by the entered coverage in square feet per US gallon per coat.
Copy the coverage for the product and planned surface into the field. Confirm it with the painter when reviewing the material list. Treat the starting value as an editable example. The calculator does not identify the surface, choose coats, or adjust coverage on your behalf.
## Read gallons before rounding the order
For example, 640 square feet minus forty-two square feet of exclusions leaves 598 square feet. Two coats produce 1,196 square feet across coats. At 350 square feet per US gallon with ten percent waste, the estimate is about 3.76 US gallons, rounded upward to four whole US gallons.
The tool keeps the unrounded quantity through the whole-gallon calculation. Do not round each wall before adding the areas. Zero waste adds no allowance. Estimate primer separately, and confirm the actual container sizes with the supplier before translating the result into an order.
## Check the inputs and results
| Input | Unit and accepted values |
| --- | --- |
| Gross surface and excluded area | Square feet, 0 through 1,000,000 |
| Excluded area | Cannot exceed gross surface area |
| Coats | Whole count, 1 through 10 |
| Product coverage per coat | Square feet per US gallon, 0.000001 through 10,000 |
| Waste | Percent, 0 through 100 |
Keep the excluded area within the gross surface area. Enter a whole coat count and positive product coverage. The whole-gallon option rounds the full adjusted quantity upward.
## Before you order paint
Label the quantity as US gallons. [NIST’s unit table](https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8) distinguishes US and Imperial gallons. Use the selected product’s coverage in the matching unit.
Ask the painter about preparation before fixing coverage. [Sherwin-Williams’ hard-surface guidance](https://www.sherwin-williams.com/architects-specifiers-designers/deck-products/resources/SW-ARTICLE-PRO-PEELINGOVERHARD) addresses adhesion, while [USG’s finishing paper](https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/finishing-decorating-gypsum-panels-white-paper-en-J2010.pdf) addresses gypsum preparation. Keep primer as a separate estimate.
For renovation, review the applicable [EPA lead-safe requirements](https://www.epa.gov/lead/renovation-repair-and-painting-program-contractors) before disturbing existing paint. Track permit questions through the [local inspection office](https://raleighnc.gov/permits/services/residential-inspections); a quantity result establishes no approval.
Discuss the surfaces with the [painting sub](/trades/painting/) and product compatibility with the [drywall and coatings supplier](/suppliers/drywall/). Use the [drywall finish-level guide](/guides/drywall-finish-levels/) for the preparation handoff.
Return to the [construction tools hub](/tools/) for the other quantity checks and printable records.
## Where Cercha fits
Use the Cercha app’s Search filters to find a painting trade. Review portfolio photos and use Messages to discuss the surfaces and finish scope. Keep product names, colors, and quantity assumptions with that conversation.
- Gross paintable surface (ft²): 350
- Area not painted (ft²): 0
- Coats (count): 1
- Product coverage per coat (ft² / US gal): 350
- Waste allowance (%): 0
Net area (ft²): 350.000000; Area across coats (ft²-coats): 350.000000; Gallons with allowance (US gal): 1.000000; Estimated paint (US gal): 1.00; Whole US gallons: 1
## How this is calculated
Net area = gross surface − excluded area. Coated area = net area × coats. Gallons = coated area × (1 + waste percent ÷ 100) ÷ product coverage. Whole gallons = ceiling(gallons).
Areas are square feet. Coverage is square feet per US gallon per coat. Apply coats and allowance before dividing and rounding.
Areas and gallons show six decimal places. The main estimate shows two. Round the unrounded gallon quantity upward to whole US gallons.
Ordinary displays round half up: an exact halfway value rounds upward. Display rounding never changes the purchase ceiling.
[Sherwin-Williams: Painter Skills Program, presenter notes](https://images.sherwin-williams.com/content_images/sw-pdf-painter-skills-training-class-presentation-presenter-notes.pdf). Net wall area; gallons = area / coverage; one-coat assumption; extra coats; typical coverage 350-400 ft2/gal. Use explicit coverage input.
Estimate only. Use coverage from the selected product. Different surfaces may require different coverage or coats. Whole US gallons are the chosen packaging mode. Confirm actual packaging and quantities before ordering.
Estimate only. No structural sizing, loads, spans, strengths, or code-compliance decisions are calculated.
Quantity estimate only. Enter product coverage per coat. Run separate estimates for each product, color, and primer. Confirm packaging before ordering.
Print this calculator from the HTML page.
## Build your connections
[Ask about the beta]()
## Sources
1. Sherwin-Williams. (2023). *Painter Skills Program: Presenter Notes*. https://images.sherwin-williams.com/content_images/sw-pdf-painter-skills-training-class-presentation-presenter-notes.pdf
2. NIST. (2025, August 18). *Guide to the SI, Appendix B.8*. https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8
3. U.S. Environmental Protection Agency. (2026, March 31). *Renovation, Repair and Painting Program: Contractors*. https://www.epa.gov/lead/renovation-repair-and-painting-program-contractors
4. Sherwin-Williams. (n.d.). *Peeling - Over Hard, Slick Surfaces*. Retrieved October 14, 2026, from https://www.sherwin-williams.com/architects-specifiers-designers/deck-products/resources/SW-ARTICLE-PRO-PEELINGOVERHARD
5. USG Corporation. (2022, July). *Finishing & Decorating Gypsum Panels*. https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/finishing-decorating-gypsum-panels-white-paper-en-J2010.pdf
6. City of Raleigh. (2026, October 12). *Residential Inspections*. Raleighnc.gov. https://raleighnc.gov/permits/services/residential-inspections