Many DIY’ers have a hard time determining the amount of paint required for painting a room or a portion of interior painting. There are really only two factors that determine paint quantity:
1. How many square feet does the paint cover per gallon?
2 How many square feet am I going to paint?
Painting ceilings and walls
The amount of paint required for ceiling and walls is a simple equation if the ceiling and walls are going to be painted the same color.
You will usually get about 400SF to a gallon of paint (per coat) on smooth walls like drywall, sheetrock or plaster.
You need to calculate the square footage of each room:
1. each wall: (length X height)
2. ceiling: - If you are painting the ceiling (length X width)
Once you know the square footage, you will multiply that number by the number of coats you intend to apply (x2 for two coats, x3 for three coats etc...), next, divide that number by 400 (SF per gallon of paint) and you will have the number of gallons you will need.
If the ceiling is going to be painted a different color than the walls, you will need to keep a separate tally for the ceiling and another for the walls, but the calculation will be done the same way for each - as explained above (i.e. Total SF / 400 = Gallons)
Painting Trim and Doors
If the trim is going to be painted a separate color (it often is) or in a different paint (such as enamel), then you will need to calculate the trim separately from the walls / ceiling.
You will get approximately the same - 400SF per gallon (per coat) for trim painting as you would on walls, but you will not have as clean a number for the square footage to be painted. Most trim will be measured in linear feet, because it is narrow. Doors and larger items, like shelving and wainscoting should be totaled a square footage, then you will need to sharpen you pencil to get the square footage of the narrow trim.
Convert linear feet to square feet
Think of linear feet as a percentage or fraction of a full square foot. A piece of trim that is 4’ wide is .33 of a foot (wide), therefore, one foot of this trim= 1 x .33 or .33 SF.
Converting inches to
a percentage
1” = .083
2” = .166
3” = .25
4” = .333
5” = .416
6” = .50
7” = .583
8” = .666
9” = .75
10” = .833
11” = .916
A rule of thumb
If you don’t want to go through the trouble of calculating the trim square footage, a rule of thumb would be a quart of enamel per room + doors and large enameled items. Which is to say, an “average” room would use about a quart (per coat) to do the baseboard, casings and window frames and say maybe one entry door. This is very much a “rule of thumb” and it could be off if you have a lot of windows to be painted, or doors or simply extra “trim” (crown moulding, and chair rail moulding etc…)
EXAMPLE. (9 X 12 Room)
- wall 1: 9 X 8= 72SF
- wall 2: 12 X 8=96SF
- wall 3: 9 X 8=72SF
- wall 4: 12 X 8=96SF
- ceiling 9 X 12= 108SF
Total SF in the above example room: 72 + 96 + 72 + 96 + 108= 444SF Number of coats (we will use 2 for this example) 444 X 2 = 888 SF
Divide this total 888 / 400 (SF per gallon) = 2.22 gallons (buy 2 gallons if you want to cut it close, or 3 gallons if you want to be safe and have some left over for touch up later on down the road).
22
x 7
154
24 / .33=
Painting and Decorating Concourse Home > Interior Painting Tips > Calculate How Much Paint is Needed
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