Paint Calculator for Basement

A basement is the hardest interior room to paint, because the walls are often bare concrete, block or previously unpainted drywall that drinks the first coat. Porous masonry is the key fact here: coverage per gallon drops sharply on bare block, a primer coat is almost always needed, and the first coat can use far more paint than the second. This page works out exactly how much paint that takes, for a 20 ft × 16 ft, 8 ft ceilings basement in eggshell finish from Sherwin-Williams — and it starts with the warning that matters most. The result here is an estimate, not a guarantee: coverage and prices vary by brand, finish, surface and region, and the can label on the product you buy governs. A basement that measures the same on paper can need very different amounts of paint once the finish, the surface and the number of coats are counted, which is why every figure below is a range.

For this job the two coverage ranges that matter are the Sherwin-Williams eggshell finish range, 300–350 sq ft per gallon (about 28–33 sq m per 3.79 L), and the masonry surface range, 150–250 sq ft per gallon. The worked example uses the finish range, and the surface range is the check that keeps the answer honest.

How the calculation works

The calculator needs five inputs, and each one changes the answer. First, the wall area: wall area is the perimeter times the height: 2 × (20 + 16) = 72 ft of wall × 8 ft high = 576 sq ft, minus 20 sq ft for two small windows and the stair opening, giving 556 sq ft (51.7 sq m). Second, the number of coats: two coats is the plan here, because one coat rarely gives an even finish, especially when the colour is changing. Third, the finish: eggshell paint from Sherwin-Williams covers a typical 300–350 sq ft per gallon in our data, and glossier finishes generally cover slightly more per gallon than flat ones. Fourth, the surface: masonry covers a typical 150–250 sq ft per gallon, and porous or rough surfaces sit at the low end. Fifth, the brand: Sherwin-Williams is the brand used for this worked example, and its price range is given by region in the cost section below. The formula is short: gallons = wall area × coats ÷ coverage per gallon, calculated twice — once at the high end of the coverage range for the low gallon count, and once at the low end for the high gallon count. Always round up to whole gallons: paint is sold by the gallon, and a half-gallon shortfall at the end of a job is the most expensive kind of shortfall.

Worked example: a 20 ft × 16 ft, 8 ft ceilings basement

Here is the full arithmetic for a 20 ft × 16 ft, 8 ft ceilings basement, two coats of eggshell paint on masonry, using Sherwin-Williams.

Step 1 — paintable area. wall area is the perimeter times the height: 2 × (20 + 16) = 72 ft of wall × 8 ft high = 576 sq ft, minus 20 sq ft for two small windows and the stair opening, giving 556 sq ft (51.7 sq m).

Step 2 — area to cover. Two coats means the paint has to cover 556 × 2 = 1112 sq ft (103.3 sq m) of surface in total.

Step 3 — gallons at each end of the range. At the high end of the 300–350 range: 1112 ÷ 350 = 3.2 gallons. At the low end of the same range: 1112 ÷ 300 = 3.7 gallons.

Step 4 — buy range. Rounded up, that is 4–5 gallons for two coats. Buy the high end if the surface is rough, the colour change is large, or you are rolling rather than spraying, and keep a little back for touch-ups.

Step 5 — the surface check. On masonry the typical coverage range is 150–250 sq ft per gallon, which is consistent with the finish range used above. If your basement is bigger, scale the same way: measure again, multiply by two coats, divide by the same range, and round up again.

Cost guidance

For Sherwin-Williams, the typical retail range per gallon in our data is Northeast $50–$90; Midwest $45–$85; South $45–$80; West $50–$90 per gallon. Across all four regions that is roughly $45–$90 per gallon, so 4–5 gallons works out at roughly $180–$450 for the paint itself — a typical retail range, check the current shelf price before budgeting. That figure is for paint only: primer, rollers, brushes, tape, drop cloths and caulk are separate, and premium lines from the same brand sit at the top of the range while mid-tier lines sit lower. Prices also move with promotions and with the retailer, so the shelf price on the day you buy is the only price that counts. Buy the paint and the primer from the same trip if you can, and keep the receipt: an unopened gallon is returnable at most retailers, which makes buying the high end of the range a low-risk decision.

Step by step: measure, calculate, order

1. Measure the basement. Measure every wall at its longest point, and measure the height from floor to ceiling in at least two places, because floors and ceilings are rarely perfectly level. Write each measurement down in feet and inches, convert inches to decimal feet (6 in = 0.5 ft), and sketch the room on paper with the measurements marked.

2. Deduct what you will not paint. Subtract doors, windows and any large built-in area from the wall total, and note the surface: smooth drywall, textured plaster, bare wood or masonry, because the surface changes the coverage range. For a basement, the deductions are the difference between a right answer and an answer that is a gallon too high.

3. Use the calculator on this page. Enter the wall area, the number of coats, the finish and the surface, and use the paint calculator to get a range, not a single number. Check the result against the can label for the exact product you buy: if the label states a lower coverage range than the one used here, plan on the high end of the gallon range.

4. Order and check the cans. Buy the high end of the range, all from the same batch if possible, and check the labels before you leave the store: same brand, same product line, same colour code, same finish. Keep one unopened gallon for returns and a small labelled jar for touch-ups.

5. Before you open a can. Clean the walls, fill and sand any holes, tape the edges, and stir the paint thoroughly. Paint the ceiling first, then the walls, then the trim, and keep the room ventilated while the paint dries.

Common mistakes to avoid

The most common mistake with a basement is measuring the floor and calling it the wall area — the walls are what you paint, and they are usually two to three times the floor area. The second mistake is buying the low end of the range and then running out with one wall left, which costs a second trip and sometimes a second batch that does not quite match. The third is skipping the second coat on the grounds that the first coat looks fine while it is still wet; paint dries lighter and thinner than it looks, and the second coat is what gives an even finish. Finally, do not paint over dust, grease or flaking old paint and expect the new coat to hold — a quick clean and a light sanding cost an hour and save a repaint. Measure twice, buy the high end of the range, and keep a little paint back for touch-ups in a labelled jar.

Frequently asked questions

How many gallons of paint do I need for a basement?

For the worked example on this page — a 20 ft × 16 ft, 8 ft ceilings basement, two coats of eggshell paint — the answer is 4–5 gallons. The range exists because Sherwin-Williams eggshell coverage varies across the 300–350 sq ft per gallon range, so measure your own basement and divide by the same range.

Is one coat enough for a basement?

Usually not. One coat can look fine while it is wet, but it dries thinner and patchier than it looks, and the colour underneath often shows through in places. Two coats are the standard for a {room}, and the second coat is what gives the even finish the first coat promises.

Which finish should I use for a basement?

For a basement, eggshell is the usual choice: it balances washability against a low-glare look, and it hides small wall imperfections better than a glossier finish. Flat or matte finishes hide imperfections most effectively but are harder to clean, while semi-gloss and gloss are tougher but show every bump.

How much does it cost to paint a basement?

For 4–5 gallons of Sherwin-Williams, the paint itself works out at roughly $180–$450 — a typical retail range, check the current shelf price before budgeting. Primer, rollers, brushes, tape and drop cloths are extra, and hiring the work out is quoted separately.

Do I need primer before painting a basement?

On a previously painted {room} in good condition, primer is usually needed only on patches and repairs. On bare drywall, stained walls or a sharp colour change, a full primer coat is worth it: it seals the surface so the topcoat covers evenly in two coats instead of three.

Related calculators

Results are estimates — verify with the product label. Coverage, pack sizes, yields and prices vary by brand, product line, surface and region; the label on the product you buy governs. Cost figures are typical retail ranges — check the current shelf price before budgeting.