To calibrate a sprayer, measure how much water it actually delivers over a known area or time, then adjust speed, pressure or nozzle size until it matches the volume per hectare on your herbicide label. Skipping this is the most common reason a correctly mixed herbicide still fails or burns the crop.
Why calibration matters
A label rate such as "2 L of product in 200 L of water per hectare" only works if your sprayer really applies 200 L/ha. A worn nozzle can deliver 10–20% too much; a walking pace that is too fast can deliver far too little. Too little means poor weed control and faster resistance; too much wastes product, risks crop injury and breaks the label.
What you need
- A clean sprayer filled with plain water (never herbicide for calibration)
- Measuring jug (1 L), stopwatch or phone timer
- Tape measure and marker stakes
- Calculator and a notebook
Method 1: Backpack sprayer (the 100 m² test)
- Mark a test plot. Measure out 10 m × 10 m (100 m²) on similar ground to your field.
- Fill the tank to a known level, e.g. exactly 5 L, and pressurise as you normally would.
- Spray the plot at your normal walking pace and swing width, keeping the nozzle at normal height.
- Refill to the original mark using the measuring jug. The water you added is what you applied.
- Convert to hectares: litres used × 100 = litres per hectare.
Worked example: A hectare is 10,000 m², which is 100 plots of 100 m². If you used 2 L on the plot, you apply 2 × 100 = 200 L/ha. If the label wants 200 L/ha, you are calibrated.
Method 2: Nozzle catch test (boom or lance)
- Run the sprayer at working pressure.
- Catch the output of one nozzle for exactly 60 seconds.
- Repeat for every nozzle. Replace any nozzle that is more than 10% above or below the average.
- Use the formula below to find litres per hectare.
L/ha = (litres per minute per nozzle × 600) ÷ (speed in km/h × nozzle spacing in metres)
Worked example: 1.2 L/min per nozzle, 5 km/h, 0.5 m spacing: (1.2 × 600) ÷ (5 × 0.5) = 720 ÷ 2.5 = 288 L/ha. To reach 200 L/ha, you can speed up to about 7.2 km/h or fit a smaller nozzle.
Calibration cheat sheet
| Problem found | Likely cause | Fix |
|---|---|---|
| Output too high | Worn nozzles, pressure too high | Replace nozzles, lower pressure, walk faster |
| Output too low | Blocked filter, pace too fast | Clean filters, slow down, larger nozzle |
| Uneven nozzle outputs | Damaged or mixed nozzle types | Fit a matched set of the same size |
| Streaky coverage | Wrong boom height or spacing | Follow nozzle maker's height guide |
Mixing after calibration
Once you know your sprayer delivers, say, 200 L/ha and your tank holds 15 L, one tank covers 15 ÷ 200 = 0.075 ha. Multiply the per-hectare product rate by 0.075 to get the dose per tank. Always follow the product label. Our guide to how much herbicide you need covers dilution in more detail.
Pro tip: Re-calibrate at the start of each season and whenever you change nozzles, pressure or the person spraying. Pace varies between people.
Watch out: Always wear gloves and eye protection, and rinse the sprayer thoroughly before and after use. Read the Safety Data Sheet for every product.
Frequently Asked Questions
How often should I calibrate my sprayer?
At the start of every season, after changing nozzles or pressure, and whenever a different operator takes over. A quick catch test takes about five minutes.
Can I calibrate with herbicide in the tank?
No. Always calibrate with clean water to avoid wasting product and exposing yourself unnecessarily.
What is a normal water volume per hectare for herbicides?
Many post-emergence herbicides call for roughly 100-300 L/ha, but the label for your specific product is the only figure that counts.
Ready to treat your land? Browse the full HerbiSolutions herbicide range.