Granular Applicator Calibration & kg/ha from a Catch Test
Calibrates spreaders
Catch the granules over a measured strip, weigh them, and get the actual kg/ha plus how far off the target you are — so you adjust the gate or speed to within ±5%.
Calibrate the applicator
Next: the applicator is within ±5% — good to go.
Catch the granules over a measured strip (swath × distance), weigh them, and scale to kg/ha; recheck after any speed or gate change.
Granular calibration — key facts
- Actual rate
- catch ÷ test area → kg/ha
- Test area
- length × width (or rows × spacing)
- Deviation
- actual vs target, %
- Target
- within ±5%
- Drive faster
- lowers the rate
- Open the gate
- raises the rate
- Recalibrate when
- product, batch or speed changes
- Privacy
- Runs in your browser; nothing uploaded
Put on the labelled rate, not a guess
Granular insecticides and fertilisers only work at the rate on the label — apply too little and the pest survives or the crop goes hungry, too much and you waste product, scorch plants and risk residues. But applicators drift off-rate as granules, gate settings, ground speed and wear all change. The fix is a catch test: run the applicator over a measured strip, catch the granules instead of dropping them, weigh the catch, and scale it to kilograms per hectare.
This tool gives the actual kg/ha, the test area, the deviation from target and the target itself from your catch weight and strip measurements — then tells you whether to open the gate, close it, or change speed to land within ±5%. Re-run after each adjustment, and recalibrate whenever the product, batch or conditions change. Pair it with the Sprayer Calibration and Boom Sprayer Nozzle Output calculators for the whole application kit.
Catch and weigh
Turn a measured strip catch into kg/ha.
See the deviation
Know how far off target you are, and which way.
Dial to ±5%
Adjust the gate or speed and re-test.
Stop the waste
No over- or under-application across the field.
Frequently Asked Questions
Why calibrate a granular applicator?+
Granular insecticides and fertilisers must go on at the labelled rate — too little fails to control the pest or feed the crop, too much wastes product, damages plants and risks residues. Spreaders and applicators drift off-rate as granules, settings, ground speed and wear change. A catch test measures what you are actually applying so you can set it right before treating the whole field.
How does the catch test work?+
Run the applicator over a measured test strip — a known length of one or more rows, or a set area — catching the granules in a tray, pan or cloth instead of letting them hit the ground. Weigh what you collect, and the tool scales that catch from the test area up to kilograms per hectare. That figure is your actual application rate.
How is the actual kg/ha calculated?+
Actual rate = caught weight ÷ test area, scaled to a hectare. The tool takes the grams or kilograms you collected over the strip's area (length × working width, or rows × spacing × length) and converts to kg/ha. It then compares that to your target rate and shows the deviation as a percentage so you know which way and how far to adjust.
What deviation is acceptable?+
Aim to be within about ±5% of the target rate. A small deviation is normal and tolerable, but more than 5% means the gate, metering or speed needs adjusting. The tool flags whether you are over, under or on-rate so you can correct it before committing product to the whole field — far cheaper than discovering it after application.
How do I adjust the rate after the test?+
If you are applying too much, close the gate or metering opening a step or drive faster; if too little, open the gate or slow down. Rate scales inversely with ground speed and roughly with gate opening, so a small change in either moves the rate. Re-run the catch test after each adjustment until you land within ±5% of target.
Does ground speed matter?+
Very much. Granular applicators meter out granules over distance, so the faster you drive, the more ground each kilogram covers and the lower the rate per hectare — and the reverse when you slow down. Calibrate at the exact speed you will treat at, keep that speed steady in the field, and re-check if you change gear or terrain forces a different pace.
Do granule type and humidity affect calibration?+
Yes. Granule size, density, flowability and moisture all change how fast product meters out of the same setting, so a calibration done for one product or batch may not hold for another. Damp or humid conditions can clog or slow flow. Recalibrate whenever you switch product, open a new batch, or conditions change noticeably.
Why scale a small catch up to a hectare?+
Weighing the output over a whole hectare is impractical, so you catch over a small, measured strip and scale it. As long as the strip is representative — steady speed, normal gate, even ground — the kg/ha figure is reliable. Catch over a longer strip or repeat the test and average to reduce the error from a one-off short run.
Does this work for spinner spreaders too?+
Yes for the rate-per-hectare maths, but spinner broadcasters also need their spread pattern checked across the working width with a tray test, because granules don't land evenly edge to edge. Use this calculator for the overall application rate; check the distribution pattern separately so both the amount and the evenness are right.
Are the figures precise?+
They're as precise as your catch test. Accuracy depends on measuring the test area correctly, weighing the catch cleanly, and running at a steady, representative speed. Repeat the test, average the catches, and recalibrate when product, batch or conditions change — calibration is a routine check, not a one-time job.