You always hear that you should water your plants an inch of water a week, but what does that actually mean? Well, in order to figure out how much to water your garden, a little bit of math will be involved.

For this example, we will be working with one square foot, since “one inch of water” is used to refer to how much water it takes to cover a square foot of garden space with one inch of water. First, we need to convert our square feet into square inches. By multiplying 12” by 12”, we get 144 square inches, meaning this is how many inches of water you need to cover your given garden space. Since the world of gardening doesn’t have tools that measure in square inches, we need to convert our square inches into gallons. A gallon is equivalent to 231 cubic inches, so if you divide your number of square inches by a gallon, you will end up with the amount of water needed for your space. In this scenario, we would divide 144 by 231 and end up with 0.6 gallons of water.

You can use this process to easily find out the correct amount of water for your garden by simply figuring out how many square feet your space is!

But what about containers? This requires a little more math, and even some geometry. For this equation we will need to remember how to find the area of a circle. In short, calculate the radius of your circle, square it, then multiply by 𝜋. To keep things simple, we will use 3.14 in our equations.

I’ll use an 8” pot for this example. We need the radius of our pot to find our area (divide your diameter in half), so we will divide 8 by 2. Our planter has a 4” radius. Next, we square our radius (multiply your number by itself), so we will multiply 4×4, which gives us 16”. Lastly, multiply 16×3.14, and that will give us 50.24 square inches. Overall the equation will look like this:

=(8÷2)²x3.14

=(4)²x3.14

=16×3.14

=50.24

As we did with the last equation, we need to convert our square inches into gallons. So we will divide 50.24 by 231, and use .2 gallons to water our plant. You can use that equation to figure out how much to water your plants by simply replacing the 8 with the diameter of your pot, and then doing the rest of the math as follows.

If you find working with gallons difficult, you can convert your water inches into cups! All you have to do is multiply your amount of gallons by 16 and have the amount of cups you need to water your garden. For example, 9.6 cups for 1 square foot of space, or 3.2 cups for an 8” pot.