Joint Compound Calculator

Skim coating covers a whole wall with a thin layer of joint compound to hide imperfections before painting. The amount depends on the area, the number of coats and how rough the wall is.

The calculator uses the same wall measurement as the paint calculator and turns the result into buckets and gallons.

How to use

Enter the room or the walls, minus doors and windows. Tick the ceiling if you're skimming it.
Pick the number of coats: usually 2.
Adjust the coverage per coat if your product lists another number.
Read the total and the buckets to buy.

How far each package goes

Package	1 coat	2 coats	3 coats
4.5 gal	458 sq ft	229 sq ft	153 sq ft
1 gal	102 sq ft	51 sq ft	34 sq ft

At 101.9 sq ft/gal per coat for a thin skim coat. Rough walls take more.

Coverage of joint compound

For taping and finishing new drywall, USG lists about 9.4 gallons of ready-mixed compound per 1,000 sq ft. A full skim coat over a whole wall uses more per square foot; this calculator assumes about 100 sq ft per gallon per thin coat.

Before painting

Let each coat dry, sand lightly and remove the dust. Then prime: compound absorbs paint unevenly without it.

Where the numbers come from

Coverage and consumption figures come from manufacturer data sheets and published standards:

Frequently asked questions

How much joint compound do I need to skim coat a room?

A 12 × 12 ft room with 8 ft walls has about 350 sq ft of wall. Two thin coats at 100 sq ft per gallon need about 7 gallons: one 4.5-gallon bucket and three 1-gallon pails, or two buckets.

How many coats of skim coat?

Two thin coats are usual; a third for walls with deep damage.

Should I use all-purpose or lightweight compound?

Lightweight compound is easier to sand and spreads a little farther; all-purpose is stronger. Both work for skim coating.

Do I need to prime after skim coating?

Yes. A primer seals the compound so the paint dries evenly. See the paint calculator.