Backpack Sprayer Calibration Calculator — Litres per Hectare & Product per Tank
Calibrate a knapsack or backpack sprayer: spray a measured test area with water, get your application volume in L/ha, the area each tank covers and how much pesticide or herbicide to put in every tank.
How it works
Application volume (L/ha) = water used (L) ÷ test area (m²) × 10,000 · Product per tank = label rate (per ha) × tank (L) ÷ application volume (L/ha) · Tanks = field area × volume ÷ tank size
A backpack sprayer has no flow meter, so its output depends on your walking speed, pump strokes and nozzle. Calibrating with plain water over a measured area tells you how many litres you really put on a hectare; the product dose on the label is per hectare, so dividing it by that volume gives the amount for each tank. Recalibrate whenever you change nozzle, pressure, operator or crop height, and aim for an even 150–400 L/ha for most herbicides and insecticides.
Worked example
Spraying 1.5 L of water on a 50 m² test area means 1.5 ÷ 50 × 10,000 = 300 L/ha. A 20 L tank then covers 667 m². For a product used at 2 L/ha, each tank needs 2 × 20 ÷ 300 = 0.1333 L = 133.3 mL. A 1.5 ha field needs 22.5 tanks, 3.00 L of product and 450 L of water (32.1 gal/acre).
Sources: Alabama Cooperative Extension — The 1/128 calibration method for backpack sprayers · Ohio State University Extension — Proper calibration and operation of backpack and hand-can sprayers (FABE-531)
Frequently asked questions
How do I calibrate a backpack sprayer step by step?
Fill the tank with water, mark a test area (25–100 m²), spray it at your normal pace and pressure, then measure how much water you need to refill the tank to the starting mark. Enter the area and the water used here. Repeat two or three times and average.
What is the 1/128-acre method?
It is a US shortcut: spray an area of 340 sq ft (1/128 acre); the fluid ounces used equal the gallons per acre, because a gallon has 128 ounces. This calculator gives the same answer in litres per hectare and gallons per acre.
How many litres per hectare should a backpack sprayer apply?
Herbicides are typically applied at 150–300 L/ha and insecticides or fungicides at 200–400 L/ha with knapsack sprayers. Always follow the label, which may set a minimum water volume.
Why is my sprayer applying too much or too little?
Walking speed has the biggest effect — walking 20% faster cuts the volume by 20%. Worn or clogged nozzles and irregular pumping also change output. Keep a steady pace and pressure and check the nozzle flow regularly.
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This calculator is for educational purposes. Double-check important results before acting on them.