To calculate the approximate water volume in your pond involves simple arithmetic. There are common two ways to accomplish this approach. The first is numerical approximation, where one takes the rough measurements of the ponds and finds an estimate of the volume. The second is through direct observation, where one times how long it takes to fill the pond and a container of known volume. The benefit to the latter is that it give a much more accurate estimate of the full volume of the pond. The drawback to the fill-method is that it can only be done during whole-pond fills. The drawback to the numerical approximation is that assumptions made in the calculations create an unrefined estimate, which is usually high. These two methods are outlined below.
Method 1: Numerical Approximation
To calculate a numerical approximation of the volume of a pond, first imagine the pond is a rectangle. Some ponds are shaped like an 'L,' and in that case you could imagine the pond as two rectangles. The approximate surface area of the pond is the length times the width of the rectangle(s). To get a volume, then multiply this surface area by the depth. The best depth to use is the average depth of the pond, but this is difficult to calculate, but we can find an estimation of this depth if we take the shape of the pond into account. For most ponds that have terraced edges that step down to the deepest surface, the average depth of the pond is usually roughly 3/4 of the maximum depth. For ponds that have gently sloping walls all the way down to the deepest surface, making a triangle in the cross-section, the average depth of the pond will be ½ the maximum depth. If you are unsure of the shape or how best to estimate the average depth of your pond, you can use the maximum depth in a pinch. The maximum depth will result in a high estimate as well.
If you used feet and inches in the measurement of the length, width and depth, divide the inches by 12 and add this to the number of feet for any one measurement. When you multiply the three measurements together, the result is in cubic feet. To convert cubic feet to gallons, multiply the number of cubic feet by 7.48.
Any one measurement, length, width or depth, in feet and inches:
(inches / 12) + feet = decimal feet
Length x Width x Average Depth = Volume in cubic feet
Volume in cubic feet x 7.48 = Volume in gallons
For other unit conversions, such as converting cubic feet into liters or cubic meters, see our conversion factors page.
Method 2: Direct Observation
This method, as stated above, requires that the pond is empty and is going to be filled. In order to measure the volume of your pond using this method, you should have some means of measuring time in seconds and minutes and a large container of a known volume, such as a five gallon bucket or 50-gallon trash can. First, we assume that the rate at which water comes out of your spigot is constant. It is best to describe this method in a series of steps:
- Step 1: Fill the container of known volume with water, measuring the amount of time it takes to fill.
- Step 2: Fill your empty pond with the same hose fittings and water spigot and measure the amount of time it takes to fill.
- Step 3: Divide the time result from step 1 by the time result from step 2.
- Step 4: Multiply this number by the known volume of the container filled in step 1. That is the volume of your pond.
time to fill pond
--------------------- x volume of container = volume of pond
time to fill container
For unit conversions, such as converting gallons into liters or cubic feet, see our conversion factors page.
If you are looking for ways to calculate other helpful quantities when considering building your pond, see our Helpful Calculations page.