As a landlord, do you ever just guess how much paint you will need to paint a room in your rental unit? Do you ever end up with not enough paint or way too much? A good rule of thumb is to know that a gallon of paint covers a surface area of around 300 to 400 square feet.

Determining The Surface Area Of The Walls Of A Room

You’ll need a tape measure to determine the surface area of a room. The area of one wall can be determined by measuring the height from the floor to the ceiling and then the length along the bottom of the wall. So, take these measurements. Area is determined by multiplying height by length when determining the area of a rectangle. So, if your walls are all rectangles, this will be easy.

Let’s say one wall is 8 feet tall and 20 feet long. All you do to figure out the area of that wall is multiply 8 by 20 to get the surface area. So, in this example, the wall would have an area of 160 square feet. If the opposite wall has the same dimensions, then the opposite wall would also have an area of 160 square feet.

Then move on to the other two walls. Let’s imagine they are 15 feet long. Let’s assume that their height is 8 feet tall as well, because you have a flat ceiling. You’d figure out the area of each of these last two walls by multiplying 15 by 8. So, the third and fourth walls that you measured in this example scenario would each have a surface area of 120 square feet.

Add all four areas together to determine the square footage that you need to paint: 160+160+120+120=560.  You can measure the area of any large windows or walls and subtract that amount of square footage to get an even more accurate figure too! In our example, the surface area of the walls of the room would be 560 square feet. So, two gallons of paint will be needed to cover the walls in this example room.

Calculating The Surface Area Of Walls In A Room With An Angled Ceiling

If your ceiling is angled, you don’t have to just guess about area. You simply need to do a little more calculating.

Let’s take our previous example room, except, let’s say that the height on one of the 20 feet walls is 12 feet while the opposite wall is 8 feet.

In this more complicated situation, you simply calculate the areas by breaking the shape of the wall into two separate areas: One rectangle and one right triangle.

Figuring out the area of a right triangle may trigger flashbacks of high school geometry, but don’t worry, there are now online calculators that you can use. To figure out the area of a right triangle, you only need to have a measurement of two of the sides. So, for our wall, the tall side of the wall is 12 feet, but the short side of the wall is 8 feet. That’s a difference of 4 feet. That means the height of our triangle is 4 feet. The length is still 20 feet, as we are assuming the same length from the first example.

Use the second free area calculator located online here. Input 4 for side a and 20 for side b. The calculator says that in our example, the triangle part of the wall is 40 square feet. We had already determined that the rectangular part of the wall is 160 square feet. Add these areas together and you get a combined area for this wall of 200 square feet. The opposite wall would also have an area of 200 square feet if they are the same size.

Now you have two more walls to go, but they’re simply rectangles. One of those walls is 15 feet long by 8 feet tall:

The other is 15 feet long and 12 feet wide.

Next, add up the square footage all four walls: 200 + 200 + 120 + 180 = 700

Now, while two gallons might cover 700 square feet of surface area, you’re probably safer buying three gallons, unless you have large doors or windows that won’t need to be repainted.


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Paces Funding is a hard money lender offering hard money loans to purchase and renovate non-owner occupied residential and commercial properties throughout the Atlanta, Nashville, Florida, or the North and South Carolina metropolitan areas. Our application process for hard money loans is easy. Just fill out this very simple online form and you will be contacted shortly. Unlike other lenders, the window between applying and funding is very small. We have funded properties in as a little as one day, but typically funding hard money loans takes about seven to ten days.

Call us at 404-814-1644 or contact us online to find out whether you might qualify for this type of funding. In the meantime, check to ensure that you meet our loan criteria. Our loan amounts can be up to 65 percent of the after-repaired value of the collateral—and if you use the loan for renovation or construction, the loan amount can be based on the collateral’s improved value.