Deck Paint Calculator – How Much Paint You Need
Painting a deck feels simple until you stand in the shop staring at tins, unsure whether one will do or three will leave you short.
Deck Paint Calculator
One gallon covers about 300 square feet per coat. The answer is rounded up to whole gallons, so you always have enough.
The trick is measuring before you buy.
Paint covers about 300 square feet per gallon for one coat, so the maths is just area times coats, divided by 300.
This free deck paint calculator does that maths for you, in gallons and litres, so you buy enough paint or stain for a smooth, even finish.
Measure the deck edge to edge, count the coats you want, and the answer is exact gallons — no guessing at the shop counter.
It works for paint and stain alike, because both use the same area and coats maths.
How to Use This Calculator
Example
Let us paint a deck that is 12 feet long and 20 feet wide, with two coats.
First the area: 12 times 20 is 240 square feet.
Two coats means double the coverage: 240 times 2 is 480 square feet of paint.
Divide by 300 square feet per gallon: 480 divided by 300 is 1.6 gallons.
You cannot buy part of a gallon, so round up to 2 gallons — about 7.6 litres.
Buy 2 gallons for this deck, and you will have a little spare for touch-ups.
Now try a smaller deck: 10 feet by 10 feet is 100 square feet.
One coat needs 100 divided by 300, which is 0.33 gallons — so round up to 1 gallon.
That single gallon covers the whole small deck, with a little left for the edges.
Remember the rule: area times coats, divided by 300, rounded up.
The Bottom Line
A good deck finish starts with the right amount of paint.
Too little, and the second coat runs out halfway across the boards. Too much, and tins sit open in the shed until they go to waste.
Measure once, pick your coats, and let the calculator round up to whole gallons. The finish will look even, and the job will feel calm from the first brush stroke.
Keep the calculator open on your phone while you measure, and buy with confidence.
A deck painted with the right amount looks fresh for longer, and you will not waste a drop.
Paint in dry weather, stir the tin well, and let each coat dry before the next.
Frequently Asked Questions
Why does the calculator round up to whole gallons?
Paint is sold in whole gallons, so a part gallon is no use at the till. Rounding up also leaves a little spare for touch-ups and thin spots.
How much paint does one gallon cover?
About 300 square feet for one coat on a smooth deck. Rough or weathered boards soak up more paint, so two coats are often the safer choice.
Should I count the gaps between deck boards?
No. Measure the deck edge to edge as one rectangle, and the small gaps will be covered by the rounding up to whole gallons.
Do I need one coat or two?
One coat suits a light refresh over sound paint. Two coats give a fuller, longer-lasting finish, especially on bare wood or a deck that has weathered.
What is the difference between paint and stain?
Paint sits on top of the wood and hides the grain with solid colour. Stain soaks in and lets the grain show through, while still adding colour and protection.
Can I use this calculator for stain too?
Yes. Stain uses the same area and coats maths, so enter your deck size and coats and use the gallons result for stain just as you would for paint.
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