Once identification of the nuisance plant population has been determined, it is necessary to accurately
estimate or measure the size of the intended treatment area. Chemical application rates will be provided
on the label in either an amount to apply per surface area (acre) OR per volume (acre-foot) of water.
One acre is a surface area measurement of 43,560 square feet. One acre-foot is a volume measurement of
43,560 cubic feet (one surface acre of water one-foot deep).
Shoreline areas, square or rectangular ponds: Determine acreage by multiplying average length (in feet)
times average width (in feet) and dividing by 43,560.
FORMULA: Avg. Length (ft.) X Avg. Width (ft.)/43,560=Acres
Example #1: A rectangular pond measures 350 feet long and 200 feet wide. To calculate acreage:
(350 x 200) / 43560 = 1.6 Acres
Circular Ponds: Determine acreage by squaring the diameter, dividing the answer by 43,560 and multiplying by 0.8.
Diameter (ft.) x Diameter (ft.) x (.8) / 43560 = Acres
Example #2: A circular pond measures 235 feet across. To calculate acreage:
(235 x 235 x .8)/43,560 = 1.0 Acres
Elliptical Ponds: Determine acreage by multiplying overall length (ft.) times maximum width (ft.), dividing by
43,560 and multiplying the answer by 0.8
Length (ft.) x Width (ft.) x (.8) / 43560 = Acres
Example #3: An elliptical pond is 325 feet long across the middle and 135 feet wide. To calculate acreage:
(325 x 325 x .8)/43,560 = .8 Acres
Where only shoreline treatments are required (for example, a 20 acre lake may only need 5 acres of shoreline treatment),
it is necessary to measure shoreline length.
Along relatively straight shorelines, multiply shoreline length (in feet) times the width (in feet) of the treatment
areas (see Figure 1).
Along irregular shorelines it may be necessary to roughly divide the treatment area into rectangular sections, determine
the acreage of each and add them together to get the total acreage (see Figure 2).
To determine acre-feet of water, multiply the acreage by average depth (in feet):
Acre feet = Acreage x Average Depth (ft.)
In bodies of water having a relatively uniform bottom slope (see Figure 3), average depth can be approximated by dividing
the maximum depth by two:
Average Depth = Maximum Depth / 2
More accurate determinations can be made by taking a number of evenly spaced depth measurements throughout the intended
treatment area (see Figure 4). Total the measurements and divide by the number taken. This is also how you determine
the average depth for ponds with uneven bottoms:
Average Depth= (Total of the Depth Measurements Taken)/(Number of Depth Measurements Taken)
In ponds where water volume (gallonage) is known, acre-feet can be calculated by dividing total gallons by 326,000
(the number of gallons in an acre-foot):
Acre Feet = Total Gallons of Water / 326,000
Determining acreage and depth of treatment areas can be done very simply if scaled maps are available.
Contour maps for many public lakes can be purchased from map companies or obtained from the State.
Aerial photos from Regional Planning Commissions, the Soil Conservation Service or other resource agencies are
also helpful in measuring larger areas. Grading survey maps or landscape blueprints are often available for
larger man-made impoundments.
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