Understanding your result
The headline is the materials cost for the job including tax, and the sub-line is the tax. The three figures show the paint on its own, everything else (primer, supplies, tax) and either the cost per square foot (in area mode) or the cans.
The breakdown runs from the area and the gallons needed through the cans to buy, the paint at your price, the primer and its cans, the supplies, the subtotal, the tax and the total, then two derived figures: the all-in cost per gallon bought, which is what the paint really cost you once the extras and the rounding are in, and the cost per square foot in area mode.
The paint is usually the biggest line and the rounding is usually the surprise. The can size optimizer compares the pail, gallon and quart prices at your store for the quantity you need; the supplies calculator replaces the lump sum with an itemised list; and the painter cost estimator puts the materials figure next to what a professional would charge for the same walls.
How we calculate this
In area mode the gallons are the same arithmetic as the wall paint calculator: area divided by coverage, times coats, plus the standard 5% allowance. The rounding to cans follows the site’s rule from the can sizes page: quarts up to a gallon, gallons up to four, and a 5-gallon pail beyond that. The price is per gallon bought, which is why the all-in figure per gallon is higher than the shelf price once supplies, primer and tax are spread over the cans.
The tax is applied to the whole materials bill at the rate you enter; US state and local sales taxes on paint run from zero to about 10%. In metric mode the prices are per litre and the cans are 1, 2.5, 5 and 10 litres. The can sizes guide explains the buying maths, and the painters’ charges guide explains why the materials are a small share of a quote.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Paint price | $40 per gallon | A mid-range interior wall paint at US home-improvement stores in 2025; the spread is $25 to $70+ |
| Primer price | $25 per gallon | Multi-purpose latex primer, 2025 |
| Supplies | $60 | A roller set, brush, tape, drop cloths and filler for one room; the supplies calculator itemises it |
| Sales tax | 7% | A typical combined US state and local rate; 0 to about 10% in practice |
| Coverage and allowance | 350 sq ft per gallon, 5% | As the wall paint calculator |
| Can rounding | quarts, gallons, 5-gallon pails | The can sizes page |
Assumptions last reviewed October 7, 2026.
The calculator does not model contractor discounts, which can be 20 to 40% off shelf prices, store sales, or the return of unopened cans, which many stores accept for untinted paint. It prices one paint; a job with wall paint, ceiling paint and trim enamel is three runs, or the whole-house estimator with its price fields.
Two worked examples
One room’s walls, from the area
700 sq ft of wall at two coats and 350 sq ft per gallon, paint at $40 a gallon, $60 of supplies, 7% tax, no primer.
- Paint: 700 ÷ 350 × 2 × 1.05 = 4.2 gallons, buy a 5-gallon pail
- Paint cost: 5 × $40 = $200
- Subtotal: $200 + $60 = $260
- Total: $260 × 1.07 = $278.20
- All-in per gallon bought: $55.64; per sq ft: $0.40
The pail costs $40 more than the 4.2 gallons used, which is why the result’s note points at the can size optimizer: if the store sells gallons at $40 and the pail at $185, four gallons and a quart is the cheaper buy.
A whole floor with primer, from the gallons
1,500 sq ft of wall at 400 sq ft per gallon, premium paint at $55, 4 gallons of primer at $28, $120 of supplies, 8.25% tax.
- Paint: 1,500 ÷ 400 × 2 × 1.05 = 7.88 gallons, buy a pail + 3 gallons (8 gallons), $440
- Primer: 4 gallons × $28 = $112
- Subtotal: $440 + $112 + $120 = $672
- Total: $672 × 1.0825 = $727.44; $0.48 per sq ft
Three gallons of paint with a gallon and a quart of primer, no supplies and no tax, for comparison, is $151.25: the primer’s 1.2 gallons rounds to a gallon and a quart at $31.25.
Where to find your inputs
Area. Net wall area from the wall paint calculator, or the square footage calculator for several rooms. Use the gallons mode if you already have the quantity from any calculator on this site.
Price. The shelf or website price for the exact line and sheen; sheen changes the price. Pail prices are per pail; divide by five for the per-gallon figure.
Primer. The gallons from the primer calculator and the primer’s own price.
Supplies. A lump sum, or the itemised total from the supplies calculator.
Tax. Your combined state and local sales tax rate; zero where paint is untaxed or you have a resale exemption.
Common mistakes
- Pricing the gallons used instead of the gallons bought. 4.2 gallons costs 5 gallons’ worth.
- Forgetting primer. It is a separate can and a separate price, and skipping it costs a coat of paint.
- Ignoring supplies. Sixty dollars is a sixth of a one-room materials bill.
- Comparing materials with a quote. Materials are a fifth of a quote; the rest is labour.
- Using a pail price as a gallon price. Divide by five.
- Buying premium paint for a ceiling. Flat ceiling paint at half the price does the job.
Questions people ask
- How much does the paint for a room cost?
- A 12 × 14 room's walls, about 700 sq ft at two coats and 350 sq ft per gallon, need 4.2 gallons, which buys a 5-gallon pail. At $40 a gallon that is $200, plus $60 of rollers, tape and drop cloths and 7% tax, so about $278 in materials. Ceiling paint and trim enamel are extra cans.
- What does a gallon of paint cost?
- Interior wall paint runs from about $25 for a basic line to $70 or more for a premium one; primer about $20 to $35; trim enamel $40 to $70; exterior paint $35 to $80. Enter your store's price, because the spread between lines is larger than any average.
- Why does the calculator price 5 gallons when I need 4.2?
- Because more than four gallons is cheaper and simpler as a 5-gallon pail than as five single cans, and the site rounds that way everywhere. If your store prices pails badly, the can size optimizer compares the pail, gallon and quart prices and finds the cheapest combination.
- Should I include primer?
- If the primer calculator says the surface needs it, yes, with its own price. Primer is cheaper per gallon than paint and often saves a coat of it, which is why a change from dark to light usually costs less with primer than without.
- What supplies do I need?
- A roller frame and covers, a tray and liners, a 2 in angled brush, painter's tape, drop cloths, filler and a sanding sponge. Around $60 for one room if you have nothing; the supplies calculator itemises it by job size and lets you set the prices.
- Is materials cost most of a painting job?
- No. Materials are typically 15 to 25% of a professional quote; labour is the rest. A $278 materials bill for a room implies a quote of roughly $1,100 to $1,900, which is what the painter cost estimator reports for a room of this size.