Understanding your result
The headline is the paint for the coats you chose, with the 8% allowance, and the sub-line is the can list. The three figures show the paintable area, the tallest wall and the cans. The tallest wall figure drives the warning in the notes: under 12 ft nothing is said, between 12 and 20 ft the result suggests how to reach the top, and above 20 ft it says scaffold.
The breakdown lists each wall as width times height, the total, the openings and the paintable area, then the standard coverage, coats, allowance, total and can lines. For a wall that slopes with the stairs the height you entered is an average, which is why the arithmetic shows a round number rather than a triangle.
The quantity will be modest, a gallon or two, because a stairwell is tall but narrow. The hours will not be: the painting time calculator counts tall walls at a lower production rate, and the production rates guide explains why cutting in along a sloping ceiling line takes twice as long per foot as a level one. The ceiling over the stairwell, if there is one, is in the ceiling paint calculator.
How we calculate this
The average-height method is exact for a wall whose top edge is a straight slope: a trapezoid of width w with heights a and b has the area w × (a + b) ÷ 2. For an open stairwell where the wall runs from the lower floor’s ceiling to the upper floor’s ceiling, the heights are typically about 8 ft at the bottom and 17 to 18 ft at the top (8 ft plus the floor structure plus another 8 ft), so the average is about 12.5 to 13 ft. The default of 17 ft for both walls is a stairwell with a full-height wall on both sides. Measuring any of this is covered in the measuring guide, and the wall square footage calculator takes six walls if the stairwell has more.
Openings are the door at the bottom, any door or window on the landing, and the open side of the landing where the wall stops, at 20 sq ft per door and 15 per window from the standard sizes page. The coverage and the rounding are the same as for every wall calculator; the coverage rates table has the published figures.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Wall 1 | 12 × 17 ft | A full-height stairwell wall in a house with 8 ft ceilings and a floor between |
| Wall 2 | 4 × 17 ft | The end wall of the same stairwell |
| Openings | 40 sq ft | A door at the bottom and a landing opening; 20 sq ft per door, 15 per window |
| Coverage | 350 sq ft per gallon | Interior wall paint data sheets (Sherwin-Williams, Benjamin Moore, Behr): 350–400 |
| Coats | 2 | Manufacturers’ recommendation for a colour change |
| Allowance | 8% | Roller loss plus the extra from pole rolling; a round figure |
| Ladder limit | 12 ft; scaffold above 20 ft | Our reading of ladder manufacturers’ guidance and OSHA’s rules on ladders on stairs; a judgement, not a regulation |
Assumptions last reviewed October 7, 2026.
The calculator does not model the ceiling, the balustrade or the stair trim, which are separate products, and it does not decide how you reach the wall. The height warning is advice, not a safety standard; the room painting guide has the order of work for a stairwell that connects two floors being painted at different times.
Two worked examples
A standard two-storey stairwell
A 12 ft long wall and a 4 ft end wall, both 17 ft high, a door and a landing opening of 40 sq ft, two coats at 350 sq ft per gallon.
- Wall 1: 12 × 17 = 204 sq ft; wall 2: 4 × 17 = 68 sq ft
- Paintable: 272 − 40 = 232 sq ft
- Per coat: 232 ÷ 350 = 0.663 gallons
- Needed: 0.663 × 2 × 1.08 = 1.43 gallons, buy 1 gallon + 2 quarts
The result’s note says the 17 ft wall is above ladder-on-stairs height: an extension pole does the rolling from the treads and a stairwell ladder or a plank does the cutting-in.
A double-height entrance hall
One 10 × 22 ft wall and three 9 ft walls of 10, 8 and 6 ft, no openings entered, two coats.
- Walls: 220 + 90 + 72 + 54 = 436 sq ft
- Per coat: 436 ÷ 350 = 1.246 gallons
- Needed: 1.246 × 2 × 1.08 = 2.69 gallons, buy 2 gallons + 3 quarts
Three gallons is the sensible buy, and the 22 ft wall is scaffold work: the result says so, and the paint is the smallest cost of that wall by a wide margin.
Where to find your inputs
Widths. Along the baseboard or the stringer at the bottom of each wall. For a wall that turns a corner at a landing, enter the two parts as two walls.
Heights. For a vertical wall, floor to ceiling. For a wall that follows the stairs, measure or estimate at the lowest and highest points and enter the average; a laser measure from the landing reaches the high point without a ladder. For a wall that rises through an open stairwell, the top is the upper floor’s ceiling.
Openings. Doors at 20 sq ft, windows at 15, and the open side of a landing as width times height of the gap in the wall. Leave blank for none.
Coverage and coats. From the can; two coats for any colour change.
Common mistakes
- Using the lowest height for a sloping wall. The average, not the minimum; the wall is a trapezoid.
- Forgetting the landing opening. Where the wall stops and the balustrade starts, there is no wall to paint.
- Standing a ladder on the stairs. Use an adjustable-leg stairwell ladder, a plank, or a scaffold tower.
- Painting the stairwell a different colour from the hall. There is usually no corner to stop at; the two run together.
- Underestimating the cutting-in. The sloping ceiling line and the balustrade take longer than the rolling.
- Skipping the ceiling. It is in the ceiling calculator, and it is where the roller spatter from the tall walls ends up.
Questions people ask
- How much paint does a stairwell take?
- A typical two-storey stairwell has a long wall of about 12 × 17 ft and a short end wall of 4 × 17 ft, with a door and a landing opening of about 40 sq ft between them. That is 232 sq ft to paint, 1.43 gallons for two coats at 350 sq ft per gallon, so a gallon and two quarts.
- How do I measure a wall that slopes with the stairs?
- Measure its height at the lowest point and at the highest, average the two, and use that as the wall height with the full width. A wall that is 8 ft high at the bottom step and 17 ft at the top landing is a 12.5 ft wall for the area. The arithmetic is exact for a straight slope.
- What height needs a scaffold?
- Above about 12 ft a ladder standing on stairs is unsafe, and above 20 ft nothing but a scaffold tower or a hired crew is sensible. Between 12 and 20 ft, a stairwell ladder with adjustable legs, or a plank between a ladder and the landing, reaches the cutting-in while an extension pole does the rolling from the stairs.
- Does a tall wall take more paint per square foot?
- No, the paint goes on at the same rate; the calculator only raises the allowance to 8% because rolling on a long pole wastes a little more. What changes is the time. The painting time calculator uses a lower production rate for tall walls because of the ladder work.
- Should I use the same paint as the hallway?
- Usually, and the same colour, because the stairwell walls run into the hall walls with no corner to change colour at. Buy it as one lot so the cans match; the hallway's own quantity comes from the wall paint calculator and the two should be added before buying.
- Can I enter more than four walls?
- Enter the biggest four, then run the calculator again for the rest, or use the wall square footage calculator, which takes up to six walls and gives an area you can type into this one as a single wall with any width and the matching height.