Buying paint is easy, but you've got to figure out how much paint to buy. You have to know the condition of the walls, ceiling and/or trim you'll be painting, and whether you need a coat of primer first. You also want to include enough paint for touch-ups later on. This is true whether you're hiring a professional painter or plan to do-it-yourself.
This article starts with the preparation every painting project needs in order to be sure you're happy with the results. The best results come from good prep, good paint, and a good brush and/or roller.
We've created a worksheet to help you calculate how much paint to buy before you begin your project. It can be very frustrating to run out of paint and have to go back to the store. You also don't want to buy too much paint, since disposing of paint may not be easy depending on your town's regulations.
Prepping for a Painting Project
The quality of any painting project is based on attention to detail. The paint surface must be prepared properly. You need to fill in nicks and cracks with spackle, and caulk where the walls touch doors, windows and trim.
You also want to use a quality paint and apply it with a quality paintbrush, both of which you should purchase at a paint store where the staff can answer other questions you might have.
Pick paint to buy in colors and finishes that fit your lifestyle, i.e. “easy to wash” finishes for high traffic areas. Here are the basics for what finish works where.
- Walls are usually flat (low traffic) or satin (high traffic) finish.
- Ceilings are usually flat and by using the same color throughout your house, you can save on paint.
- Trim is most often semi-gloss, or high gloss if you want a very hard/shiny surface.
Next comes the preparation, which can greatly change the way the paint looks when done. In fact, most people assume that all you do is get some paint and one coat does it all. This couldn't be further from the truth. You've got to repair imperfections first, then go over rest of the surface to get good adhesion of your final paint coat.
- Patch holes, sand rough spots, and use a primer on new sheet rock. Use a stain block like Kilz as needed.
- Apply 2 coats when painting unfinished or heavily patched walls, or when covering dark colors.
- Do not use cheap paint (minimum $20/gallon) or you'll need to apply an extra coat of paint, which ends up costing more.
- Buy some extra paint for small repairs by rounding up to the nearest gallon. (The cost of a gallon is usually about the same as 2+ quarts, so you might as well just purchase the gallon.)
It's always hard to know which tools get the best results, so here are ones recommended by friends who are professional painters meaning they do this every day.
Calculating How Much Paint to Buy
Here's a worksheet to help determine how much paint to buy. The example is for a 10 x 14 ft room with 2 doors, 2 windows and ceiling height of 8 ft (average). Most paint covers 350 sq ft per gallon, but it's best to review the label, especially when using a paint that says it only needs one coat.
| Sample WALL Calculation | Sample Room | Room #1 | Room #2 | Room #3 |
| Add length of all walls = linear ft (LF) | 48 lf | |||
| Multiply LF x ceiling height = sq ft | 384 sq ft | |||
| Subtract doors (20 sq ft/door) | 344 sq ft | |||
| Subtract windows (15 sq ft/window) | 314 sq ft | |||
| For 2 coats, multiply by 2 | 628 sq ft | |||
| Add 10% contingency | 691 sq ft | |||
| Divide by 350 sq ft/gallon | 2.0 gal |
| Sample CEILING Calculation | Sample Room | Room #1 | Room #2 | Room #3 |
| Use 2 longest walls for ceiling sq ft | 168 sq ft | |||
| For 2 coats, multiply by 2 | 336 sq ft | |||
| Add 10% contingency | 370 gal | |||
| Divide by 350 sq ft/gallon | 1.1 gal |
| Sample TRIM Calculation | Sample Room | Room #1 | Room #2 | Room #3 |
| Calculate the LF for all 4 walls, including closets with baseboard | 48 lf | |||
| Add door trim (20 lf/door for sides + door width for top trim) | 88 lf | |||
| Add window trim (use 15 lf/window) | 118 lf | |||
| Calculate LF x 0.5 (6 in) to get sq ft | 59 sq ft | |||
| Add 10% contingency | 0.2 gal |
And we've got lots more painting articles. Here are ones you might find helpful right now:
- Types of Paint Finishes: Matte, Eggshell, Satin …
- Paint Colors and Lighting
- Painting Mistakes You Don't Want to Make
- How to Safely Dispose of Paint
thank you for this informative blog keep sharing
Great article, I love this comment “The best results come from good prep, good paint and a good brush and/or roller”. The benefit of prep cannot be overemphasized. people want a good result without doing the work it takes to get there.
You can’t get a good straight line with a wonky cutting brush is how I like to put it
Leanne, It is incredibly important to use the right tools & especially a good paint brush. I went to a workshop the other night on Annie Sloan paints. They made me use a yucky brush on half the pumpkin … and then a good brush for the other half. It was a good way to show the difference a brush can make.
This is very helpful post for contractors like me who are weak in math. Simply bookmarked it for later use. Thanks for this.
Glad you like it & think you might find a calculator online now … as I wrote this post almost 10 years ago. I’ll have to update soon.
Its all depends on the type of paint or its thickness. Anyway, I love reading this kind of mathematical blogs.
Hmm, Never thought of this as mathematical but maybe … LOL. I should probably update this article with links to some online paint calculators that didn’t exist when I wrote this article.
And it’s important to always have a little paint left over for touching up later on – even if you go back to the store and purchase the exact same colour they can look slightly different from batch to batch on the wall.
You’re absolutely right that you can’t match the paint color because it’s mixed slightly differently. When you have multiple cans of the same color, you are supposed to mix the paint between the cans to avoid this problem … and then as the paint fades it becomes ever more challenging.
I just want someone to double check my math?!
I want to paint different color squares on a wall. There are 44 squares, measured at 1 sq ft each. If I need 2 coats for each square, that means I have a total of 88 squares to paint. Add the 10% contingency, that brings me up to 97 — so I’ll round it up to 100 sq ft that I want to color.
Since I want multi-colors, I thought that maybe I can get away with buying multiple sample paint which comes in 7.5 fl. oz containers for $4 each at Home Depot. If my math is correct, then I would spend only $20 in paint, instead of $15+ per quart of paint (per color).
There are 128 fl. oz in 1 gallon (of paint), and 1 gallon of paint covers 350 sq ft. Therefore:
350 sq ft = 100 sq ft
———– ————
128 oz 7.5 oz * X
where X = number of cans of 7.5 oz sample paint I would need to cover a 100 sq ft wall.
Crunch the number, and I get 4.876… round up to 5.
Therefore, I will need 5 cans of 7.5 oz sample paint.
Am I right? Or am I way off? is there another contingency I should worry about? Like, I don’t really get to use all 7.5 oz in a jar because some of it gets left behind in the bucket/can, etc… ??
Jackie, You’re certainly being creative here & your numbers are fine … but I definitely wouldn’t do what you’re planning. The problem is you’ll get uneven paint buildup along the lines (4 coats) and the more you try to correct problems from going over the lines, the more layers you’ll add and the surface won’t be flat.
You should paint the entire wall with one of your colors, i.e. to start with nice flat surface. Then wait at least a week until this paint is really dry. Then you can use tape (test until you’ve learned to lay tape down well to prevent bleeding) or draw lines, to paint your second color.
For this type of project, I’d suggest using 20% contingency and I listen to my professional painters and they use Benjamin Moore or Sherwin Williams.
Tina – do you have any idea what % of interior paint jobs in the house are done by women? How about exterior?
Les, Fascinating question & certainly one worth asking. I don’t have any hard statistics but if you allow me to guesstimate, I would say only 10 to 20% of exterior paint jobs are done by women. There are quite a few reasons for this but #1 is women are much better at detail, which isn’t as important outside the house, and very important inside. Attention to detail takes more time and costs more, so women painters primarily focus on the work they like and do well at, and many more women painters also do faux painting.
The challenges of exterior painting start with how much work is done from a ladder. More important, it’s the equipment you have to balance on the ladder from pressure washing hoses to paint sprayers which are commonly used to paint wood siding as brush and rollers, except for trim, would take way too long.
This question always arise that how much paint to buy for your place because this will directly related to your budget but for this you have to talk to person who is experienced in this field.For more details contact to our team of professional painters.
Wow!! This is really best top for home painting contractors and home painting consumers.