★ CONSTRUCTION · PAINT · REFERENCE TABLE
A 12 x 12 ft room takes 2 cans. That is 384 sq ft of wall, 1.10 gallons raw and 1.21 gallons with 10% waste, at $90.00 for two $45 cans. The 9-inch roller is the standard for walls, with a 3/8-inch nap on smooth walls — pick a size in the chart, or price any room below.
Pick a roller width for the room and a nap for the wall, or enter the room and let the calculator count the paint: the wall area is two times the length plus the width, times the height, times the coats; the gallons are the area divided by the coverage, plus waste, rounded up to whole cans — so the number you get is the number to buy.
Every standard roller width, with what it is best for and the nap length to pair it with. The bigger the roller, the fewer passes a wall takes: an 18-in roller covers twice the width of a 9-in roller per pass, a 12-in roller is 1.33 times the 9-in width, and a 4-in roller is 0.44 times it. The 9-in roller is the standard for walls, and the most common size in the chart.
| Roller width | Best for | Nap range |
|---|---|---|
| 4 in | trim, doors, cabinets, small areas | 3/8–1/2 in nap |
| 6 in | small rooms, bathrooms, trim | 3/8–1/2 in nap |
| 9 in | standard walls, most common size | 3/8 in nap (smooth) to 1/2 in |
| 12 in | large walls, big rooms | 3/8–1/2 in nap |
| 18 in | commercial jobs, large flat areas | 3/8–3/4 in nap |
The nap is how long the roller cover's fibres are, and it sets how much paint the roller holds and how far it reaches into the wall. A short nap suits a smooth wall; a long nap suits a rough one. This chart is explicitly not a sprayer or airless chart, and not a paint-type chart: roller sizes and nap only.
| Nap length | Surface |
|---|---|
| 1/4 in | smooth surfaces |
| 3/8 in | smooth / semi-smooth, the standard |
| 1/2 in | semi-rough |
| 3/4 in | rough / textured |
| 1 in | very rough |
Paint gallons are three steps: the wall area, the coverage of the paint, and the waste on top of it. The wall area is two times the length plus the width, times the ceiling height, times the coats, in square feet — the two comes from the room having two pairs of walls. Divide by the coverage in square feet a gallon, add the waste percent for spillage and touch-ups, then round up to whole cans — you cannot buy part of a can, and running short mid-wall is the expensive mistake.
At the defaults — a 12 x 12 ft room, 8 ft ceiling, 1 coat, 350 sq ft/gal, 10% waste, $45/gal — the wall area is 2 × (12 + 12) × 8 × 1 = 384 sq ft, the raw gallons are 384 ÷ 350 = 1.10 gal (1.0971), the billable gallons are 1.0971 × 1.10 = 1.21 gal (1.2069), and the cans are 1.2069 rounded up to 2 cans, at 2 × $45 = $90.00. The recommended roller for 384 sq ft is 9 in, and the nap for a smooth wall is 3/8 in.
| Case | Wall area (sq ft) | Raw (gal) | Billable (gal) | Cans | Cost |
|---|---|---|---|---|---|
| Default (12 x 12 ft, 8 ft, 1 coat) | 384 | 1.10 | 1.21 | 2 | $90.00 |
| 2 coats | 768 | 2.19 | 2.41 | 3 | $135.00 |
| 10 x 10 ft room | 320 | 0.91 | 1.01 | 2 | $90.00 |
| 20 x 15 ft room | 560 | 1.60 | 1.76 | 2 | $90.00 |
| 30 x 20 ft room | 800 | 2.29 | 2.51 | 3 | $135.00 |
| 20 x 15 ft, 2 coats | 1,120 | 3.20 | 3.52 | 4 | $180.00 |
| Coverage 400 sq ft/gal | 384 | 0.96 | 1.06 | 2 | $90.00 |
| Coverage 300 sq ft/gal | 384 | 1.28 | 1.41 | 2 | $90.00 |
| Waste 0% | 384 | 1.10 | 1.10 | 2 | $90.00 |
| Price $35/gal | 384 | 1.10 | 1.21 | 2 | $70.00 |
| Price $60/gal | 384 | 1.10 | 1.21 | 2 | $120.00 |
| 9 ft ceiling | 432 | 1.23 | 1.36 | 2 | $90.00 |
| 10 ft ceiling | 480 | 1.37 | 1.51 | 2 | $90.00 |
Setup: 12 x 12 ft room, 8 ft ceiling, 1 coat, 350 sq ft/gal, 10% waste, $45/gal, smooth wall.
Line 1 — the wall area. 2 × (12 + 12) × 8 × 1 = 384 sq ft.
Line 2 — the raw gallons. 384 ÷ 350 = 1.10 gal (1.0971).
Line 3 — the billable gallons. 1.0971 × 1.10 = 1.21 gal (1.2069).
Line 4 — the cans. 1.2069 rounded up to 2 cans.
Line 5 — the cost. 2 × $45 = $90.00.
Line 6 — the roller and the nap. 384 sq ft is between 150 and 600 sq ft, so the roller is 9 in; a smooth wall takes a 3/8 in nap.
Reverse: a $45 budget buys 1 can, or 350 sq ft; a $90 budget buys 2 cans, or 700 sq ft; a $100 budget buys 2 cans, or 700 sq ft; a $135 budget buys 3 cans, or 1,050 sq ft; a $180 budget buys 4 cans, or 1,400 sq ft. One gallon covers 350 sq ft in one coat, and 5 gallons cover 1,750 sq ft. 1,000 sq ft in one coat needs 2.86 gal raw, 3.14 gal billable, 4 cans, $180.00.
2 coats: two coats double the wall area to 2 × (12 + 12) × 8 × 2 = 768 sq ft, the raw gallons are 768 ÷ 350 = 2.19 gal (2.1943), the billable gallons are 2.1943 × 1.10 = 2.41 gal (2.4137), and the cans are 3 cans at $135.00. Two coats is not quite twice the paint, because the rounding lands differently.
10 x 10 ft room: the wall area is 2 × (10 + 10) × 8 = 320 sq ft, the raw gallons are 320 ÷ 350 = 0.91 gal (0.9143), the billable gallons are 0.9143 × 1.10 = 1.01 gal (1.0057), and the cans are 2 cans at $90.00. A smaller room still needs 2 cans, because one can covers only 350 sq ft.
20 x 15 ft room: the wall area is 2 × (20 + 15) × 8 = 560 sq ft, the raw gallons are 560 ÷ 350 = 1.60 gal, the billable gallons are 1.60 × 1.10 = 1.76 gal, and the cans are 2 cans at $90.00. A big room is still a two-can job at one coat.
30 x 20 ft room: the wall area is 2 × (30 + 20) × 8 = 800 sq ft, the raw gallons are 800 ÷ 350 = 2.29 gal (2.2857), the billable gallons are 2.2857 × 1.10 = 2.51 gal (2.5143), and the cans are 3 cans at $135.00. Over 600 sq ft the roller moves up to 12 to 18 in.
20 x 15 ft, 2 coats: the wall area is 2 × (20 + 15) × 8 × 2 = 1,120 sq ft, the raw gallons are 1,120 ÷ 350 = 3.20 gal, the billable gallons are 3.20 × 1.10 = 3.52 gal, and the cans are 4 cans at $180.00. Two coats on a big room is a four-can job.
Coverage 400 sq ft/gal: paint that covers further needs less of it: the raw gallons are 384 ÷ 400 = 0.96 gal, the billable gallons are 0.96 × 1.10 = 1.06 gal (1.056), and the cans are 2 cans at $90.00. Better coverage still needs 2 cans, because one can covers only 400 sq ft.
Coverage 300 sq ft/gal: paint that covers less needs more of it: the raw gallons are 384 ÷ 300 = 1.28 gal, the billable gallons are 1.28 × 1.10 = 1.41 gal (1.408), and the cans are 2 cans at $90.00. Thicker paint still lands on 2 cans for this room.
Waste 0%: with no waste the billable gallons are the raw gallons themselves, 1.10 gal (1.0971), and the cans are 2 cans at $90.00. Skipping the waste saves nothing here, because the cans round up the same way.
Price $35/gal: cheaper paint changes the cost, not the cans: 2 cans at $70.00. The gallons are the same 1.10 raw and 1.21 billable.
Price $60/gal: dearer paint changes the cost, not the cans: 2 cans at $120.00. The gallons are the same 1.10 raw and 1.21 billable.
9 ft ceiling: a taller ceiling adds wall area: 2 × (12 + 12) × 9 = 432 sq ft, the raw gallons are 432 ÷ 350 = 1.23 gal (1.2343), the billable gallons are 1.2343 × 1.10 = 1.36 gal (1.3577), and the cans are 2 cans at $90.00. One more foot of ceiling is 48 sq ft of wall.
10 ft ceiling: 2 × (12 + 12) × 10 = 480 sq ft, the raw gallons are 480 ÷ 350 = 1.37 gal (1.3714), the billable gallons are 1.3714 × 1.10 = 1.51 gal (1.5086), and the cans are 2 cans at $90.00. Two more feet of ceiling is 96 sq ft of wall, and still 2 cans.
Reverse — the budget and the gallons: a $45 budget buys 45 ÷ $45 = 1 can, or 1 × 350 = 350 sq ft; a $90 budget buys 2 cans, or 700 sq ft; a $100 budget buys 100 ÷ $45 = 2 cans, or 700 sq ft — the $10 left over buys no can; a $135 budget buys 3 cans, or 1,050 sq ft; a $180 budget buys 4 cans, or 1,400 sq ft. One gallon covers 350 sq ft in one coat, and 5 gallons cover 1,750 sq ft. 1,000 sq ft in one coat needs 1,000 ÷ 350 = 2.86 gal raw (2.8571), 2.8571 × 1.10 = 3.14 gal billable (3.1429), 4 cans, $180.00.
The model assumes four flat walls of even height, the same coverage for every coat, and the same waste percent across the job. It assumes one coat unless you say otherwise, and it leaves out primer, trim, ceilings, doors, windows and the second coat, which change the gallons in real life. The roller recommendation follows the wall area only: under 150 sq ft a 4 to 6 in roller, 150 to 600 sq ft a 9 in roller, and over 600 sq ft a 12 to 18 in roller. The nap follows the wall surface only: smooth 3/8 in, semi-smooth 1/2 in, textured 3/4 in. Rounding convention: areas are whole square feet, gallons are shown to two decimals, cans are always rounded up to a whole can, and money is rounded to cents, all computed from unrounded values.
| Output | Formula | What it means |
|---|---|---|
| Wall area | 2 × (length + width) × height × coats | 384 sq ft. |
| Raw gallons | area ÷ coverage | 1.10 gal. |
| Billable gallons | raw × (1 + waste%) | 1.21 gal. |
| Cans to buy | ceil(billable) | 2 cans. |
| Cost | cans × price/gal | $90.00. |
| Recommended roller | by wall area | 9 in. |
| Nap | by wall surface | 3/8 in for a smooth wall. |
| 2 coats | same model, 2 coats | 768 sq ft, 2.19 gal raw, 2.41 gal billable, 3 cans, $135.00. |
| 10 x 10 ft room | same model, 10 x 10 ft | 320 sq ft, 0.91 gal raw, 1.01 gal billable, 2 cans, $90.00. |
| 20 x 15 ft room | same model, 20 x 15 ft | 560 sq ft, 1.60 gal raw, 1.76 gal billable, 2 cans, $90.00. |
| 30 x 20 ft room | same model, 30 x 20 ft | 800 sq ft, 2.29 gal raw, 2.51 gal billable, 3 cans, $135.00. |
| 20 x 15 ft, 2 coats | same model, 20 x 15 ft, 2 coats | 1,120 sq ft, 3.20 gal raw, 3.52 gal billable, 4 cans, $180.00. |
| Coverage 400 sq ft/gal | same model, 400 sq ft/gal | 384 sq ft, 0.96 gal raw, 1.06 gal billable, 2 cans, $90.00. |
| Coverage 300 sq ft/gal | same model, 300 sq ft/gal | 384 sq ft, 1.28 gal raw, 1.41 gal billable, 2 cans, $90.00. |
| Waste 0% | same model, 0% waste | 384 sq ft, 1.10 gal raw, 1.10 gal billable, 2 cans, $90.00. |
| Price $35/gal | same model, $35/gal | 384 sq ft, 1.10 gal raw, 1.21 gal billable, 2 cans, $70.00. |
| Price $60/gal | same model, $60/gal | 384 sq ft, 1.10 gal raw, 1.21 gal billable, 2 cans, $120.00. |
| 9 ft ceiling | same model, 9 ft ceiling | 432 sq ft, 1.23 gal raw, 1.36 gal billable, 2 cans, $90.00. |
| 10 ft ceiling | same model, 10 ft ceiling | 480 sq ft, 1.37 gal raw, 1.51 gal billable, 2 cans, $90.00. |
| $45 budget | floor(budget ÷ price) | 1 can = 350 sq ft. |
| $90 budget | floor(budget ÷ price) | 2 cans = 700 sq ft. |
| $100 budget | floor(budget ÷ price) | 2 cans = 700 sq ft. |
| $135 budget | floor(budget ÷ price) | 3 cans = 1,050 sq ft. |
| $180 budget | floor(budget ÷ price) | 4 cans = 1,400 sq ft. |
| 1 gallon covers | 1 × coverage | 350 sq ft (1 coat). |
| 5 gallons cover | 5 × coverage | 1,750 sq ft (1 coat). |
| 1,000 sq ft (1 coat) | same model, 1,000 sq ft | 2.86 gal raw, 3.14 gal billable, 4 cans, $180.00. |
| 18-in vs 9-in width | 18 ÷ 9 | 2.00×. |
| 12-in vs 9-in width | 12 ÷ 9 | 1.33×. |
| 4-in vs 9-in width | 4 ÷ 9 | 0.44×. |
The math is exact for the numbers you enter: the wall area is two times the length plus the width, times the height, times the coats; the raw gallons are the area divided by the coverage; the billable gallons are the raw gallons times one plus the waste; and the cans are the billable gallons rounded up to a whole can. What the chart cannot do is measure your room for you: check the length, the width and the ceiling height on a tape, because a 9 ft ceiling and an 8 ft ceiling give different answers. It assumes flat walls, even coverage and the same waste across the job, and it leaves out primer, trim, ceilings, doors and windows. This is not a sprayer or airless chart, and not a paint-type chart. For the slab the paint goes on, see concrete slab calculator; for the cost of the pour behind it, see concrete cost calculator.
Bright Side Kit. "Paint Roller Size Chart: Sizes, Nap & Coverage 2026." https://brightoolbox.com/paint-roller-size-chart/ Accessed October 25, 2026.1.21 gallons with waste — buy 2 cans. A 12 x 12 ft room with an 8 ft ceiling is 384 sq ft of wall, which is 1.10 gallons raw at 350 sq ft a gallon, and 1.21 gallons with 10% waste, so buy 2 one-gallon cans at $90.00.
9 inches for standard walls. The 9-in roller is the most common size, and it fits rooms from 150 to 600 sq ft of wall. Under 150 sq ft use a 4 to 6 in roller; over 600 sq ft use a 12 to 18 in roller.
3/4 inch. A textured or rough wall needs a 3/4 in nap to reach into the texture. A smooth wall takes 3/8 in, and a semi-smooth wall takes 1/2 in.
Wall area, coverage, waste, then round up. The wall area is 2 times the length plus the width, times the height, times the coats, in square feet. Divide by the coverage in sq ft a gallon, add the waste percent, then round up to whole cans. At the defaults that is 384 sq ft, 1.10 gallons raw, 1.21 gallons billable, and 2 cans.
1 can, or 350 sq ft. At $45 a gallon, $45 buys 1 can, which covers 350 sq ft in one coat. $90 buys 2 cans, or 700 sq ft; $135 buys 3 cans, or 1,050 sq ft; and $180 buys 4 cans, or 1,400 sq ft.
3.14 gallons with waste — buy 4 cans. 1,000 sq ft at 350 sq ft a gallon is 2.86 gallons raw, and 3.14 gallons with 10% waste, so buy 4 one-gallon cans at $180.00.
No. This is a roller size and nap chart only — it is explicitly not a sprayer or airless chart, and not a paint-type chart. It leaves out primer, trim, ceilings, doors and the second coat, which change the gallons in real life.