# How to Measure a Water Garden

Knowing how much water a pond holds will help you determine the size of the aeration or filtration system you will need to install. It will also help you properly dose the pond with water treatments and determine how many fish the pond can house.

Luckily there are formulas that will determine the volume of water for you after you've collected a few important measurements based on the shape of the pond.

RECTANGULAR PONDS

The easiest ponds to measure are those that resemble a rectangle. First, measure the maximum length and width of the pond and then measure the pond depth. Figuring out its depth is a bit trickier, particularly if there are plant shelves or if the pond has a slope.

If it is the same depth throughout, use that number in the formula. If there is a plant shelf or the depth varies, measure the maximum depth and cut it in half to create an average depth.

For instance, let's say the pond is four feet at its deepest but has some shallow areas for plants. Use half of that depth, or two feet, for your formula.

For Example:
If the pond is 15 feet long by 10 feet wide by 2 feet deep, the pond's volume is 300 cubic feet.

One cubic foot holds 7.48 gallons of water, so multiply 300 by 7.48 to get your total - which equals 2,244 gallons.

CIRCULAR PONDS

If the pond is round or oval, start by using this formula to find the surface area of a circle which is:

Surface Area: Pi x Radius2 or 3.14 x R x R

The radius of the pond is half the distance across, so if the pond is a 10-foot circle, the radius is 5 feet. Your formula will look like this:

Radius: 3.14 x 5 x 5 = 78.5

Next, figure out the pond's depth, just like we did with the rectangular pond. If it's 4 feet deep with plant shelves and sloped sides, use 2 feet. Then multiply that number by your surface area:

Depth: 78.5 x 2 = 157 Cubic Feet

Finally, convert that number into gallons. One cubic foot holds 7.48 gallons of water so your formula looks like this:

Gallons: 157 x 7.48 = 1,174 gallons.

IRREGULAR SHAPED PONDS

The more irregular the pond's shape, the less accurate your measurement will become. In most cases, you don't need to pinpoint its volume to the exact gallon. Use whichever formula best resembles the pond's shape. For instance, if the pond is kidney-shaped, use the rectangle formula and remember that the final figure will be slightly higher.

Don't forget to take into account that some of the water from your pond will be held in the streambed, plumbing, and filters. If you want to know exactly how many gallons are in your pond you can use a meter to physically measure the amount of water it takes to fill the pond using a garden hose.  