Gallon Capacity of a Sink

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Go to any hardware or big box store and you can see that there are many different stainless steel kitchen sink sizes.
Image Credit: kitzcorner/iStock/GettyImages

Go to any hardware or big box store and you can see that there are many different stainless steel kitchen sink sizes. Sinks also come in different types, such as one or two bowls, and are manufactured with different colors and materials. One thing you can't tell by looking, however, is the liquid volume of a kitchen sink. If you want to determine your rectangular kitchen or round bathroom sink capacity, there are simple formulas that can help you figure it out.

Sink Shapes and Sizes

Kitchen sinks are usually rectangular shaped but come in many different styles, including drop-in, undermount and wall-mount. They are also available in a variety of materials, including stainless steel, copper, cast iron and granite. With a kitchen sink, you also have an option of one, two or three bowls. Kitchen sinks can be as small as 9 inches or over 40 inches in length, but a standard-size sink ranges from 24 to 36 inches.

Stainless steel kitchen sink sizes can vary. Single-bowl kitchen sinks usually measure up to 30 inches in length and can be larger, but sinks over 30 inches usually have a double bowl. Some sinks have shallow bowls, while others are deeper, which is why knowing how to determine the liquid volume of a kitchen sink is important. Bathroom sinks are usually round or oval and a different calculation is used to determine bathroom sink capacity.

Square or Rectangular Sink Capacity

Some might panic when hearing that there's a formula involved to determine the gallon capacity of a sink. But if you've taken a high school math class, then you can figure out the capacity of your kitchen sink. Even if you didn't do well in the class, you should be able to calculate the liquid volume of a kitchen sink. In fact, you've most likely heard most of it before.

To find the gallon capacity of a sink, you multiply the length by width by depth (L x W x D) of your sink bowl and divide the answer by 231, which is the cubic volume by inches in a gallon. The length is the measurement of the bowl from right to left. The width is the measurement from back to front. And the depth is the measurement from the bottom of the bowl to the top.

One thing to remember when doing your calculation is that most people don't fill their sinks all the way to the very top because it can spill over. For this reason, it's a good idea to measure the depth a couple of inches short of the top of the sink, rather than all the way to the top. When you calculate the total, divide it by 231 to find out exactly how many gallons your sink holds. If you have a double-bowl sink, you can calculate the capacity of each bowl individually.

Round Bathroom Sink Capacity

Because most bathroom sinks are round or oval and smaller in size than a kitchen sink, there is a different formula used to determine bathroom sink capacity. For a round sink, you measure the radius (the distance from the center of the sink to the edge) and square it, or multiply it by itself. Then you multiply this number by the depth, and multiply the result by 3.14. Once you have a total, you divide it by 231.

That makes the round sink capacity formula: radius x radius x depth x 3.14, then divide the total by 231. It's a little more complicated than the formula for a rectangular sink, but not that difficult in practice. If the number 3.14 looks familiar, that's because it's pi, from high school math. Looks like those teachers were right when they said we'd use it someday.


Gary Sprague

Gary Sprague

Gary Sprague is a retired master plumber who now works as a writer. He lives with his family in Maine.