Quick answer: Acres = length (ft) × width (ft) ÷ 43,560. Gallons of spray mix = acres × your spray volume in gallons per acre (GPA). Product needed = acres × the rate on your herbicide label. Enter your own numbers below. The tool does the math in your browser and sends nothing anywhere.
How the math works
An acre is 43,560 square feet, and a mile is 5,280 feet. A right-of-way 1 mile long and 50 feet wide is 264,000 square feet, or about 6.06 acres. At 20 GPA that strip takes about 121 gallons of spray mix. If the label rate were 2 quarts per acre, you would need about 12.1 quarts (3.03 gallons) of product for the whole strip.
Per tank, the calculator works out how many acres one load covers (tank size ÷ GPA) and multiplies that by the label rate. A 300-gallon tank at 20 GPA covers 15 acres, so at 2 quarts per acre it takes 30 quarts (7.5 gallons) of product per full tank. For a percent-solution label, such as a spot or brush spray mixed at a set percentage, product = gallons of mix × percent ÷ 100. Surfactant works the same way.
Unit conversions used: 128 fl oz = 1 gallon, 16 fl oz = 1 pint, 32 fl oz = 1 quart, 4 quarts = 1 gallon. Dry products in pounds are not converted to gallons.
Get your GPA from calibration, not a guess
Everything above depends on spray volume. The easy field check is the 1/128-acre method. One gallon is 128 fluid ounces, so if you catch the spray a nozzle puts out in the time it takes to cover 1/128 of an acre (about 340 square feet), the ounces you catch equal gallons per acre. For a boom, the test distance depends on nozzle spacing: 204 feet for 20-inch spacing. Extension guides say to replace any nozzle that is more than 10% off the average, and to recalibrate after changing speed, pressure or tips.
The label sets the rate
The herbicide label is a legal document, and using a product in a way the label doesn't allow is a violation of federal law. That's why this tool never fills in a rate. Read the rate, the spray volume range, the surfactant directions and the max per-acre or per-year amount off your own label, then enter them. If your rate is given as a range, run the tool at both ends.
Tips for right-of-way and lease work
- Measure the width you actually spray, not the full easement, if you are only treating a strip.
- Round the tank count up and mix the last load to match the acres left, so you don't haul leftover mix.
- Check the label's minimum and maximum GPA. Some products need more water for coverage on brush.
More background: our guides on pipeline right-of-way vegetation control and oilfield lease weed control.
Sources: LSU AgCenter, Ounces Equal Gallons (43,560 sq ft acre, 340 sq ft = 1/128 acre); UNH Extension, 1/128th method; Ohio State, Boom Sprayer Calibration (FABE-520); EPA, Introduction to Pesticide Labels.
Rather hand it off? Send us the acres or the line map and we will quote the job.
Get a weed control quoteFAQ
How do you calculate acres for a right-of-way?
Multiply the length in feet by the sprayed width in feet and divide by 43,560. A strip 1 mile long and 50 feet wide is 264,000 square feet, about 6.06 acres.
How many gallons of spray mix do I need?
Multiply acres by your spray volume in gallons per acre (GPA). At 20 GPA, 6.06 acres takes about 121 gallons of mix.
How much herbicide goes in each tank?
Divide tank size by GPA to get acres per tank, then multiply by the label rate. A 300-gallon tank at 20 GPA covers 15 acres, so a 2 quart per acre rate means 30 quarts per tank.
How do I find my sprayer's gallons per acre?
Use the 1/128-acre method: time how long it takes to cover 1/128 acre, catch one nozzle's output for that long, and the fluid ounces caught equal gallons per acre.
Why doesn't the calculator suggest a herbicide rate?
Because the label sets the rate, and using a product in a way the label does not allow violates federal law. Enter the rate printed on your label.