Mix the right amount of herbicide for any sprayer. Enter the label rate per acre, per 1,000 sq ft, per gallon or as a percent solution, your tank size, spray volume and the area, and get the product per tank, the number of tank fills, the last partial tank, total product and an optional surfactant amount.
Last updated:
Label rate is given
Copy it from the product label for your weed and site.
Sprayer
How much mixed spray your sprayer puts out per area, from calibration or the label (boom sprayers often 10–20 gal/acre; hand sprayers often 0.5–2 gal per 1,000 sq ft).
Area
% v/v
Nonionic surfactants are often 0.25–0.5% (1–2 qt per 100 gal). Use only if the label allows.
Enter your values to see the result.
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How to use the Herbicide Mix Calculator
Choose how the label gives the rate: per acre, per 1,000 sq ft, per gallon, as a % solution or per hectare.
Enter the label rate and its unit.
Enter the tank size and spray volume from your sprayer calibration.
Enter the area to treat and, if the label calls for it, the surfactant rate.
Press Calculate mix to see product per tank, tank fills and the mixing plan.
Herbicide mixing formulas
Area per tank = tank size ÷ spray volume (gal per acre)
Per-acre label: product per tank = rate per acre × area per tank
Per-1,000 sq ft label: rate per acre = rate × 43.56
Per-gallon label: product per tank = rate per gallon × tank gallons
% solution: product per tank = tank gallons × % ÷ 100 × 128 fl oz
Tank fills = area × spray volume ÷ tank size
Example: 5 acres, label rate 32 fl oz per acre, 25 gallon tank, calibrated at 15 gal/acre. One tank covers 25 ÷ 15 = 1.67 acres and needs 32 × 1.67 = 53.3 fl oz of product. The job needs 5 × 15 = 75 gallons of spray, exactly 3 full tanks and 160 fl oz (1.25 gal) of product.
Handy conversions
Unit
Equals
1 US gallon
128 fl oz · 4 qt · 8 pt · 3.785 L
1 quart
32 fl oz · 946 mL
1 pint
16 fl oz · 473 mL
1 fl oz
2 tbsp · 6 tsp · 29.6 mL
1 acre
43,560 sq ft · 0.405 ha
1 hectare
2.471 acres · 10,000 sq m
1% solution
1.28 fl oz per gallon · 10 mL per liter
1 L/ha
about 0.107 gal per acre (13.7 fl oz per acre)
Mixing tips
The label is the law: use only products labeled for your site and weed, at or below the label rate.
Calibrate your sprayer at the start of each season and whenever you change nozzles, pressure or speed.
Fill the tank half full with clean water, add products in the order the label gives, agitate, then fill to the mark.
Mix only what you will use that day, and plan the last partial tank so there is little left over.
Wear the protective gear the label lists, spray on calm days, and keep children and pets away until the spray has dried or as the label directs.
Frequently asked questions
How do I calculate how much herbicide to put in my sprayer?
For a per-acre label rate, first find how many acres one tank covers: tank gallons ÷ spray volume in gallons per acre. Multiply that by the label rate. A 25 gallon tank at 15 gal/acre covers 1.67 acres, so at 32 fl oz per acre you add 53.3 fl oz of product per tank.
What does gallons per acre (GPA) mean on a spray label?
GPA is the spray volume: the total amount of mixed water and product applied per acre. It is set by your sprayer's nozzles, pressure and travel speed, so it comes from calibrating your sprayer. The product rate per acre stays the same whatever GPA you use; only the concentration in the tank changes.
How do I convert ounces per acre to ounces per gallon?
Divide the rate per acre by your spray volume. At 32 fl oz per acre and 20 gallons per acre, each gallon of spray needs 32 ÷ 20 = 1.6 fl oz of product.
How do I mix a 2% herbicide solution?
A 2% solution is 2 parts product in 100 parts total spray. One gallon is 128 fl oz, so 2% is 2.56 fl oz of product per gallon, or about 5.1 fl oz in a 2 gallon sprayer, topped up with water.
How do I convert a rate per 1,000 sq ft to per acre?
Multiply by 43.56, because one acre is 43,560 square feet. A rate of 1.5 fl oz per 1,000 sq ft equals about 65 fl oz per acre.
How do I calibrate a sprayer to find my spray volume?
Mark out a test area, such as 1,000 sq ft, fill the sprayer with water only, spray the area at your normal walking or driving speed and pressure, and measure how much water you used. That amount is your spray volume per 1,000 sq ft; multiply by 43.56 for gallons per acre.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.