Interior
Drywall and Paint Calculator
Measure the room once. This gives you the board to hang it and the paint to finish it, in the order you buy them.
| Wall area | — |
|---|---|
| Ceiling | — |
| Board area, openings out | — |
| Sheets, rounded up | — |
| Compound and tape | — |
| Paint area, openings out | — |
| Times the coats | — |
| Gallons, rounded up | — |
UNITS GAL
SOURCE /SOURCES/#room
What to buy
Paid links. If you buy through one, we earn a commission. Your price is the same. Nothing is listed here unless the calculator above says you need it.
Why this is more than you need
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Drywall sheets
The sheet count above assumes the size you picked. Longer sheets cut the number of seams you have to tape, which is the slow part of the job.
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Joint compound
The gallons above come from National Gypsum's own estimator rather than a rule of thumb. Buckets are usually 4.5 gal.
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Paper joint tape
The footage above is for the seams your sheet size produces. Paper is stronger on flats than mesh and costs less.
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Interior wall paint
The gallon figure uses the coverage you entered. Check the number on the can, because it decides the answer more than the room size does.
What the makers state
| Sherwin-Williams SuperPaint Flat A86 | 350 to 400 sq ft/gal | PDS 101.02A, 4/2025, at 4 mils wet |
|---|---|---|
| Benjamin Moore Regal Select N551 | 400 to 450 sq ft/gal | TDS N551 US 062025, 3.6 to 4.0 mils wet |
| Valspar 2000 Interior Satin 670350 | 350 to 450 sq ft/gal | PDS rev 7/29/2019, 4.0 mils wet |
| National Gypsum estimator | 9.0 gal mud, 350 ft tape per 1,000 sq ft | Drywall Materials Estimator and Coverage |
Two different industries, and the reason this page exists. The paint figures are three brands' own ranges, all quoted at about 4 mils wet so they are comparable. The finishing rates are one manufacturer's estimator, because it is the only one that publishes the whole set.
Gear for the job
The calculator above does not count any of this. It is what the job takes to actually do. Paid links, and your price is the same.
- Drywall screw gun It sets the screw to the right depth and stops. A regular driver either sits proud or tears the paper, and both have to be fixed later.
- Taping knives Three widths, because each coat is spread wider than the one under it. One knife makes every seam a ridge.
- Drywall lift or panel jack Only if you picked a ceiling above. A sheet of 4x12 overhead is a two-person job without one, and a bad idea with one.
- Pole sander Reaches the top of a wall from the floor and keeps the pressure even, which is what stops a sanded seam turning into a hollow.
- Roller frame and covers The paint half of the job. Nap thickness follows the texture you just created, so buy them after the walls are finished, not before.
- Painter's tape Sized off the room perimeter rather than the wall area, so it is not in the numbers above.
Part of a bigger job
This calculator sizes one material. These jobs need it along with others, and the list says what else to buy and in what order.
- Finish a room drywall, paint, wallpaper
The same window is 15 square feet to the painter and 20 to the drywaller, and that is not a contradiction. Drywall is cut to the framed rough opening; paint stops at the finished trim. One room, one tape measure, two different numbers, which is exactly what nobody selling a single product will tell you.
How to estimate a room's board and paint together
A manufacturer will size the one product it sells and stop. Finishing a room takes two, they are bought weeks apart, and they are measured from the same tape. This page does both from one set of dimensions.
wall area = 2 × (length + width) × height
board = wall area + ceiling − (openings × 20)
paint = wall area − (doors × 20) − (windows × 15), × coats ÷ coverageCoverage is the reader's own figure, defaulting to the 350 sq ft/gal floor that Sherwin-Williams, Benjamin Moore and Valspar all overlap on. Finishing rates are National Gypsum's published estimator.
Measure the room once
Length, width, ceiling height. The wall area is the perimeter times the height, and the perimeter of a rectangular room is twice the length plus twice the width. A 14 by 12 room is 52 feet around, so 416 square feet of wall at 8 feet.
Closets count if you are finishing them. An alcove or a bay adds its own walls, so measure the perimeter as you would walk it rather than treating the room as a plain rectangle.
The part only a combined page will tell you
The two trades subtract openings differently, and it is not sloppiness on either side.
Drywall is cut to the framed rough opening. That opening is deliberately larger than the door or window that goes into it, because the unit needs shimming room. So a door and a window are both about 20 square feet of board you do not hang.
Paint stops at the finished trim. A door is still about 20 square feet, since a stock 36 by 80 inch slab is exactly 20.0. A typical 3 by 5 foot window is 15. The casing covers the difference.
On the default room that gap is 10 square feet: 356 square feet of board against 366 of paint. That sounds trivial and it is not, because the paint figure gets multiplied by the number of coats before it meets the coverage number. Ten square feet at two coats is twenty, which is a real fraction of a gallon.
Sheets, and why the size matters more than the count
Divide the board area by the sheet area and round up. A 4 by 8 sheet is 32 square feet, a 4 by 10 is 40, a 4 by 12 is 48.
The count is the boring half. The seams are the real decision. Longer sheets span more wall in one piece, which means fewer butt joints to tape, float and sand, and butt joints are the ones that show. If you can get 12 foot sheets into the room, the taping is meaningfully easier. If the stairwell says no, that decision is already made for you.
Rounding up is not waste. Offcuts fill the small pieces above and beside openings, and spare board patches well later.
Compound, tape and screws
National Gypsum publishes the whole set as a rate: about 9 gallons of joint compound, 350 feet of tape and 1,250 screws per 1,000 square feet of board. The chart runs from 100 to 1,500 square feet and is linear across every row, so it divides cleanly for any room.
One caution, and it is the reason this page prints a rate rather than copying a table. That chart's 1,300 square foot row prints 17.7 gallons where the linear series gives 11.7. It is a transcription typo in the published document, not a real jump. We use the rate.
Compound comes in 4.5 gallon buckets, so a room is one and a floor is several. Buy the larger container for more than one room: the price per gallon drops sharply and it keeps if the lid seals.
Paint, and the number that actually decides it
Coverage decides the gallon count more than the room size does. That is why it is an editable field rather than a constant.
The default is 350 square feet per gallon. That is not an average, it is the floor of the band where three manufacturers' stated ranges overlap: Sherwin-Williams quotes 350 to 400, Benjamin Moore 400 to 450, Valspar 350 to 450. All three quote at roughly 4 mils wet, which is the only reason those ranges are comparable at all. Take the number off your own can and type it in.
Two coats is the makers' own default for a color change, and what this page assumes.
Primer is a separate purchase, and new board needs it
This calculator sizes paint, not primer, and on fresh drywall that is a gap you have to close yourself.
New board and dried joint compound drink at completely different rates. Paint straight over them dries with every seam and screw showing through as a slightly different sheen, which is the flashing everyone blames on the paint. A drywall primer or sealer fixes it in one coat over the whole area. Run the paint numbers again with one coat, at the primer's own coverage figure, to size it.
A quick cost check
The default room, walls only: 12 sheets at $18 is $216, a bucket of compound and a roll of tape about $35, and 3 gallons of paint at $40 is $120. Call it $371 in materials before primer, screws and tape knives.
Switch the ceiling on and it moves a long way: the board area goes from 356 to 524 square feet, which is 17 sheets instead of 12, and the compound goes up by half. A ceiling is a big flat area and it is the single input on this page that changes the answer most.
Common estimating mistakes
- Using one opening deduction for both materials. The board figure and the paint figure are genuinely different numbers from the same room.
- Forgetting the ceiling in the board count. It is often more area than two of the walls.
- Treating the coverage number as fixed. It is the biggest lever on the gallon count and it is printed on the can.
- Buying paint at the same time as board. Sheen and nap depend on the finish you end up with, and the board goes up weeks earlier.
- Skipping primer on new drywall. The one omission on this list that shows from across the room.
- Sizing tape off the room instead of the seams. The footage here follows the board area, which is what actually produces seams.
When to hand it off
Hanging board is heavy rather than skilled, and taping is skilled rather than heavy. Most people can hang a room and most people's first taping job looks like a first taping job, because flat, invisible seams are a genuine trade skill and sanding will not rescue a bad float.
Two real boundaries. Ceilings are worth paying for or at least renting a lift for: a sheet of 4 by 12 overhead is heavy in the worst possible position. And anything structural is not on this page at all. If a wall is coming out rather than getting covered, that is a question for someone who can tell you whether it is load bearing, and no amount of measuring substitutes for it.
Questions
How much drywall and paint do I need for a 12x14 room?
With 8 foot walls, one door and two windows, that is 416 square feet of wall. Drywall deducts 20 square feet per opening, leaving 356 square feet, so 12 sheets of 4x8. Paint deducts 20 for the door and 15 per window, leaving 366 square feet, which at two coats and 350 square feet per gallon is 2.09 gallons, so 3 gallons. The two figures differ because the two trades measure openings differently.
Why does the paint area differ from the drywall area?
Because they stop at different places. Drywall is cut to the framed rough opening, which is bigger than the finished door or window, so both count as about 20 square feet. Paint stops at the trim, and a typical 3 by 5 foot window is 15 square feet of glass and sash. On a room with several windows the two areas can differ by 10 square feet or more, which is enough to move a gallon.
Should I include the ceiling?
Board it, almost always. Paint it, only if you are painting it in the same job. The selector above separates the two for that reason: a boarded ceiling adds its full area to the sheets, the compound and the tape, but it only adds to the gallons if you tick the paint option. A ceiling is a big area, so getting this wrong moves the answer a long way.
Do I need primer as well as paint?
On new drywall, yes, and this calculator does not include it. Fresh board and dried joint compound absorb very differently, and paint alone over them shows every seam. A drywall primer or sealer is a separate product with its own coverage figure, usually one coat over the whole area. Run the paint numbers again with one coat at the primer's own coverage to size it.
How much joint compound does a room take?
About 9 gallons per 1,000 square feet of board, with 350 feet of tape, which is National Gypsum's own published rate. For a 12 by 14 room that is roughly 3.2 gallons and 125 feet of tape. Buckets are commonly 4.5 gallons, so one covers a small room. Worth knowing: their estimator chart has a typo in the 1,300 square foot row, so this page uses the rate rather than the row.
Every constant on this page is logged with its source and the date it was checked on the sources page.