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Discussion Starter · #1 ·
Hey all, coming back to the forum for my tree house for, hopefully, the last time needed. My Treehouse walls total about 400 sq ft. At an over-estimate, how many gallons of stain will i need?

PS: Will post pics of completed treehouse soon. (Its over 300 sq ft and has 2 ziplines :thumbup: )


1,402 Posts
You asked so here it goes:

Divide the stainable wall area by 350 (the square-foot coverage in each gallon can) to find the number of gallons of stain you need for the walls. You can round uneven numbers; if the remainder is less than .5, order a couple quarts of stain to go with the gallons; if the remainder is more than .5, order an extra gallon. Of course, buying in bulk is usually more economical, so you may discover that 3 quarts of stain cost as much as a gallon.

The following examples walk you through the calculations for determining how much stain you need for a 14-x-20-foot room that's 8 feet tall and has two doors and two windows.

Use the following formula to estimate the amount of stain for your ceiling you will need after all it is a tree house. Double the result if the ceiling requires two coats.

1. Multiply the length of the ceiling times its width to find its area.
14 × 20 = 280 square feet

2. Divide that number by 350 (the estimated square feet covered per gallon) to figure out how many gallons of stain you need.
280 ÷ 350 = .8

For this example, you want to buy 1 gallon of stain for your ceiling for a single coat.
Now use the following formula to estimate the amount of wall stain you will need. Double the result if the walls require two coats.

1. Add together the length of each wall.
14 + 20 + 14 + 20 = 68 feet

2. Multiply the sum by the wall height, to find the total wall area.
68 × 8 = 544 square feet

3. Subtract 20 square feet for each door (20 × 2 = 40) and 15 square feet for each window (15 × 2 = 30) to find the actual amount of wall area you're painting.
544 – 70 = 474 square feet

4. Divide this figure by the stain coverage (350 square feet per gallon), and the result is the number of gallons to purchase.
474 ÷ 350 = 1.4

For this example, you want to buy 1 gallon and 2 quarts of stain for a single coat.
If you have trim measure the length of the trim in feet, and multiply that number by 1/2 foot (.5), as a rough size for the width of the trim. Include all the trim around doors and windows, at baseboards, along the ceiling. As an example, imagine that you have ceiling molding running around a room that is 14 feet wide and 20 feet long.

1. Determine the total length of molding around the room by adding together the length of all the walls that the molding covers.
Round the numbers off to the nearest foot.
14 + 20 + 14 + 20 = 68 feet

2. Multiply the sum by .5 for an estimated width of the molding.
68 × .5 = 34 square feet

3. Divide this number by 350 to estimate the gallons of stain required to cover the molding.
34 ÷ 350 = .09

The result in this example is much less than a quart, but you may paint other woodwork in the same area, so buying a full quart may not be terribly wasteful.
Use the same figure for estimating door coverage as you use in your wall-area calculations — 20 square feet = one door. Multiply the number of doors by 20, doubling the answer if you plan to paint both sides. Wall stain estimates allow for 15 square feet for each window. Use about half that window area to figure trim and inside sash — the glass isn't important to the calculation.

For the room in this example:

1. Multiply the number of doors by 20.
2 × 20 = 40 square feet

2. Multiply the number of windows by 7.5.
2 Windows × 7.5 = 15 square feet

3. Add these numbers together.
40 + 15 = 55

4. Divide the result by 350 (the estimated square feet covered per gallon).
54 ÷ 350 = .16

Often, you end up needing to buy only a quart of paint, which goes a long way on doors and window trim.

Hope this gives you a headache lol and fine tunes your answer on how much stain to buy for your tree house project.

Painting Company, NY
1,039 Posts
This is a good formula, but you still need to know the approximate coverage of the stain that you plan on using, coverage will be different depending on some factors. 350sq feet of coverage would work to figure out how many gallons of paint are needed in most situations, most paints will cover 350-400 sq per gallon and on your second coat of paint you will use less, but some stains cover less than 350, also depending on the roughness of the wood and some cover more than 350

8 Posts
Thanks everyone! Love that formula hahaha
I stain a lot of my treehouses - it's much better than painting them. I find that the type of siding and the application method are the most important factors in the coverage.

Here's two of my "guidelines"
1. Brushing/Rolling uses more than spraying.
2. Rough textured wood uses more than smooth wood.

The answer is that you're going to need 1-2 gallons, depending on the above, since most cans are 350-400 square feet of coverage.

Here's two examples:
Treehouse #1 covered almost 600 square feet brushed and rolled and took a little over 2 gallons - had to crack the third can. Medium textured siding.

Treehouse #2 covered about 350 square feet with a cheap sprayer and used about 2/3 of a gallon. Smooth siding.
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