"How much paint do I need?" Good question. Let's make the assumption we will be talking about painting your interior sheetrock walls so we will be working with "interior latex enamel paint" for our example.....fair enough?
How much paint you need will be determined on how many square feet a gallon of paint will cover. A good rule of thumb is to figure that 1 gallon of paint will cover apprx. 300 square feet of wall.
Let's look at a room size of 12 feet wide x 16 feet long (x= the word "by"). We will assume your wall height is say 10' tall (nice ceiling height.......you must live in a great neighborhood!). Were you any good in math? Here's where your math comes into play.....you know....the math you learned in school & you always said.....what am I gonna need this for? You never knew you were going to paint some walls for yourself one day did you? Length "times" width will equal your square footage. Pay attention or you're going to fail this last math test & this time it's going to cost you money.
Here we go: add up the total length of all of the walls. In our above example (assuming you have a square room), you have a total of 56 lineal feet of wall....meaning you have 56 "running" feet of wall: 12 plus 12 plus 16 plus 16 equals 56 feet or 56'. So far so good. Now we get to do your math. Length "times" width would be 56 "running" feet of wall "times" 10 feet wall height: so we have 56 "times" 10 equals 560 feet or 560 square feet. You remember I said you should figure (as a rule of thumb) apprx. 300 square feet of wall coverage for each gallon of paint. So we would take your 560 square feet & "divide" this by 300 square feet which would equal 1.86666 gallons of paint you are going to need. It's always good to use a calculator to add things up.
Now of course you know you cannot purchase 1.86666 gallons of paint at the store. You will need to purchase 2 gallons of paint for the example above. This is where you need to pay attention: the above example is only good for "1 coat of finish paint". Ask your self the question again: "how much paint do I need?". How many coats will you be installing? If you are just freshening up the existing walls with the same paint color in the same paint finish then you should only have to install 1 coat of paint so 2 gallons of paint should be enough.
However, if you are changing the wall color or changing the finish from flat paint to semi-gloss paint,etc., you may need to install 2 coats of finish paint so you would have to "double" the order amount so you would have a total of 1120 square feet of wall area to cover so you would "divide" this by 300 square feet for a total of 3.7333 gallons of paint needed. You will need 4 gallons of paint.
This will vary if you have lots of windows in your walls or doors so plan accordingly (you could add up this square footage for windows & doors & subtract that from the total of paint needed then divide this new number to get the "actual" paint needed). You get to decide how to figure how much paint you need.
Here's some things to consider: sometimes you can almost buy 5 gallons of paint for about the same amount that you can purchase 4 gallons for. That's if you buy a 5 gallon bucket of paint rather than 4 single 1 gallon containers of paint. This varies by paint store & paint brand so do some homework & see if this applies to you. It's always wise to have a little bit of paint left over so you can save this extra paint for paint touchup down the road.
If you were to purchase a 5 gallon bucket of paint, you would have over 1 gallon of paint left over. You're in a "quandry": "should I buy more paint since I can just about buy 5 gallons of paint for the same amount as 4 gallons but do I want to store over a gallon of paint left over or......can I use that extra paint for something else & still have some paint left over for future paint touch-up?".
If you want to keep your touch-up paint in a smaller container than a 5 gallon bucket then you could purchase an empty 1 gallon paint can & lid, pour the paint into this can & save the extra paint this way. Clean out your 5 gallon bucket & save it though. You never know when it will come in handy.....for something.Think about it & make a decision. It won't be earth shattering either way but I wanted you to know you do have options.
Other things to consider: semi-gloss & gloss paint go further than flat paint. You could probably squeeze out 400 square feet to the gallon (or more) depending if it's the 1st coat or the 2nd coat. If you are painting new wall construction, then you will be needing to install a separate coat of primer & my recommendation is to then install 2 coats of finish paint over the primer. Primer will also have a tendency to soak up more into the new sheetrock so you may only get 250 square feet of paint coverage to the gallon for the primer so "do your math accordingly".
If you're looking to cut costs a bit, most paint stores have some "stock/standard" colors pre-mixed in 5 gallon containers which may work for your project. This could be ideal for your project.
Also.....yes I have more to tell you...most paint stores have "mis-matched" paint that you could use as primer (that is...if you need primer). Make sure you ask for the mis-matched paint in "flat" if you're going to do this though. You could buy however many gallons you needed (go with the lighter colors of mis-matched flat paint though), mix them altogether & you will probably come out with something like a medium beige color & you could use this as your primer (a considerable cost savings depending on how large your project is).
There you go. Measure twice, order once, use a calculator, mix & match, be prepared "before" you start your project. Do what you need to do to get your project done & in the cost frame you so desire. Options.....you have options when doing it yourself. "How much paint do I need?" You know the answer for that one!
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