How Much Interior Paint Do I Need – Do The Math Yourself

pexels blue bird 7218568 How Much Interior Paint Do I Need - Do The Math Yourself

Looking for activities to engage with your friends and family? Paint your interiors! It is an answer to dull and faded walls, transforms your space, and, more importantly, gives you cherishable moments.   

As for me, nothing gets me more excited than talking about coloring a home’s interior because indoor painting is what makes a house the HOME.

Being someone with a passion for painting, I often encounter the question: how much interior paint do I need? 

Let’s answer you right away;

To paint a room of 400 sq ft, you need one gallon can of paint. To paint a room of 800 sq ft, you need two-gallon cans of paint and so forth. If we talk about an average room size, 1 gallon can of paint easily covers the entire room with a single coat. 

Now only if things were this effortless…

I know, I know, if you’re up for a DIY job, you have so many questions racked up in your brain, and my job is to get them all answered. 

Keep scrolling to learn about all the ins and outs of the paint quantity you need to make your walls shine.

PS: Other than learning how to calculate the quantity of interior paint needed, some more nuggets of gold await you to ensure nothing goes wrong while you’re on the job. Grab them 🙂

How Much interior Paint Do I Need?

When it comes to painting indoors, there’s some measurement that goes into it. To avoid multiple trips to the store or overspending a lot of money just to see cans leftover in your garage, you need to be sure how many gallons of paint you need. 

A Rule of Thumb to Remember…
One gallon can of paint is needed for a room of 350 sq ft to 400 sq ft depending on the nature of your walls. Textured and porous walls like stucco absorb more paint.

If you can learn how to take your wall’s dimensions and follow the steps coming ahead, calculating the paint quantity will become as easy as ABC.

To make things easier to understand, we will consider the example of a medium-sized room whose length, width, and ceiling height are 12 ft, 10 ft, and 9 ft, respectively.

1. Calculate the Area of Your Room

  • Measure the perimeter of your room which is (length + width) x 2. In our case, it becomes (12 ft + 10 ft) x 2 = 44 ft.
  • To get the room’s total wall area, multiply the perimeter by the ceiling height. (44 ft x 9 ft) = 396 sq ft.

2. Calculate the Area of Windows and Doors

  • It’s obvious not to paint your windows and doors. Which means we will not include their area in our measurements.
  • An average door is 20 sq ft, and an average window is 15 sq ft. The total sq ft of the two is 35. You can measure the area of your doors and windows if you think they’re not a standard size.

3. Measure the Total Room Area Minus the Area of Doors and Windows

  • In our case, we are considering one standard door and one standard window in the room. Now our total wall area of the room becomes 396 sq ft – 35 sq ft = 361 sq ft.

4. Divide the Answer by 400

  • Since we already know that one gallon can is needed to cover 400 sq ft, we will divide the total wall area by 400, and that will be an adequate measurement of how much paint you’ll need. For our considered example, 361/400 = 0.9025. This means 1 gallon can will be enough to cover an average-sized room of 12 ft x 10 ft. 

The above measurements are for a single coat. For two coats, you can simply multiply the number of gallon cans by 2. 

Although the above steps can help you calculate the paint quantity for any dimensions, the below table will help give an estimate of some standard room sizes (the standard area of one door and one window are taken into consideration).

Room SizeRoom DimensionGallon Cans Needed
Small8 X 100.81 ≅ 1
Average9 X 120.945 ≅ 1
Large12 X 161.26 ≅ one and a half gallon 

Pop Out Your Room With Different Trim Colors

Finishing your crown moldings, baseboards, windows, doors, and ceilings in a different color than walls attracts more eyes. 

To calculate the paint needed for trims, multiply the length and width of each trim separately and add all the area measurements to get the total area of the trim. 

This may sound tiresome, but usually, trims are all the same size, so it won’t take you much time to recalculate.

Now to calculate how much paint is needed, simply divide the area by 400, and you’ll get your answer.

PS: Trims do not need much paint, so consider buying paint in quarts rather than spending on an entire gallon. Do check out the details about how to paint trims on our website. 

Time to Paint the Ceiling

To calculate the paint needed for the ceiling, just multiply the length and width of your space. Now divide this area by 400 to get your desired answer. You will likely need paint in quarts for ceilings as well. 

Let’s Calculate the Primer Needed

Did you just think of finishing your walls without a primer? That’s definitely a BIG NO, as your walls may start to crack shortly. Moreover, you will also need multiple coats of paint to finish indoors. You can read more about why primer is necessary and what happens if you skip it. 

Rule of Thumb for Primer…
You may need more primer than you need paint as one gallon can of primer covers 200 sq ft.

To calculate how much primer is required, you just need to divide your total area by 200 and the answer will give you an estimated value of the gallons. 

Go for Paint Calculators

Another way to determine the quantity of indoor paint you need to cover your spaces is to use online paint calculators. The calculator has columns that let you insert the value of your walls’ width and height and mention the doors and windows you have in the room. Moreover, you can also add measurements of the baseboards, crown moldings, and trims in the custom calculator option. After inserting all the values, press the calculate button, and there, you have it – your answer to how much indoor paint you need to coat your spaces. 

PS: Do not forget to paint the doors. You can see the best paint for interior doors and pick the right one for yours.

Some Nuggets of Gold Before You Pick Up the Brush

  • Be properly prepared with the right tools and equipment. Using the right tools can lead to less paint consumption, offer a better and smooth finish without marks, and save you time and cost. 
  • Recoloring your walls with the same old color? Just one coat of paint would do the work. Moreover, the good news is, you won’t need a primer for recoating. Hence, you will be refurbishing your home at a lower cost. 
  • Getting custom paint? Make sure to calculate exactly and get all the batches at the same time for evenly matched hues. You may also need to have a quart or two extra for future touch-ups.
  • If your walls are porous like stucco or you have unpainted dry walls, you may need more paint than calculated. While not mandatory, it is strongly recommended to apply primer to stucco walls to protect color and have consistent shade. You can learn more about priming your stucco walls. 
  • To prevent your walls from having roller lines, ensure your final stroke goes down the wall and not upwards.


How much paint do I need for a 12 X 12 room?

For a 12 X 12 room with a 9 ft height, 1.25 gallons of paint would suffice for a single coat. For multiple coats, you can multiply 1.25 by the number of coats needed. 

How much interior paint do I need for a 2000 sq ft. house?

To color a house of 2000 sq ft, you will likely need 5 gallons of interior paint. You are likely to go for a different shade for each room, so it is best to calculate separately for each room. 

How much interior paint do I need for a 1500 sq ft house?

Since 1 gallon covers 400 sq ft, to paint the indoors of a 1500 sq ft house, you will need around 4 gallons of interior paint. However, it also depends on the number of rooms and size of each room, this article covers how you can calculate it precisely to get the accurate answer.

How much interior paint do I need for a 1000 sq ft house?

A 1000 sq ft house can be easily painted with 2.5 gallons of paint. Again, it depends on the size of your rooms, bathrooms and kitchen and what exactly you want to paint. We recommend you to calculate your rooms separately to get exact answer to your question.

Is a 5-gallon can of paint cheaper than 1-gallon? 

Yes, buying a big bucket of paint will cost you less than buying single buckets individually. If you have a big job and a single color is needed, go for a bigger gallon instead of buying smaller gallons. 

Can a quart of paint cover one wall?

A quarter of paint generally covers 100 sq ft area. If the area of your wall is 100 sq ft, it can be easily covered by a quart. For estimated coverage, check out the paint container.

I have a sloping ceiling. How will I calculate the area?

A sloping ceiling makes a triangle, and to calculate its area, you need to multiply the height of the triangle by its base and divide that number by 2. Visit the link to learn more complexities on how to measure rooms with sloped ceilings. 

In a Nutshell

Painting indoors is a fun way to make the most of time with your family and friends or by yourself too. There is no exact quantity to how much paint you will need to color the interior, but a good estimate is 1 gallon for 400 sq ft. You can further calculate the area of the walls and divide that by 400 to evaluate an approx quantity of the containers needed. 

Moreover, if you are thinking of refurbishing your indoors, make sure to check out the best season to paint the interior,  and the best humidity and temperature to paint indoors so everything happens smoothly. 

Got more questions? Drop them in the comments below, and we will get back to you. 

Leave a Comment

Your email address will not be published. Required fields are marked *