---
title: Calibrating your spray rig
description: "A simple four-step spray rig calibration: check nozzles, set pressure, measure output and calculate your water rate, with a worked example and pre-spray checklist."
---

[The Farm Shed](https://www.highlandsagsolutions.com.au/the-farm-shed)

# [Calibrating your spray rig](https://www.highlandsagsolutions.com.au/the-farm-shed/calibrating-your-spray-rig)

 Written by [Will Black](https://www.highlandsagsolutions.com.au/the-farm-shed/author/will-black) | Nov 5, 2026, 4:01:38 AM

*Getting the application rate right — every time*

Autumn is the perfect time to calibrate your spray rig for the season ahead. Whether you're applying a knockdown, a residual herbicide, or a selective broadleaf product, poor calibration costs you in three ways: reduced efficacy, crop damage, and wasted chemical.

[Download this article (PDF)](https://www.highlandsagsolutions.com.au/hubfs/260303%20HAS%20Article%20-%20Spray%20rig%20calibration.pdf)

## Why calibration matters

Calibration ensures you are applying the intended litres per hectare (L/ha) at the target droplet size and pressure. Even small errors compound quickly across paddocks:

| Scenario | Error | Consequence |
| --- | --- | --- |
| **Under-application** | -10% or more | Poor weed control, resistance risk |
| **Over-application** | +10% or more | Crop stress, residue risk, wasted cost |
| **Inconsistent boom output** | Variable | Striping and patch failure |

## The 4-Step calibration process

### Step 1. Check Nozzle Condition

Before measuring anything, inspect your nozzles:

- Confirm all nozzles are the identical type and size.
- Inspect every nozzle for wear and blockage.
- Replace any nozzle that varies more than ±10% from the manufacturer's rated output.

**Watch out**

Worn nozzles are the most common cause of undetected over-application. When in doubt, replace them — nozzle sets are far cheaper than a failed spray program.

### Step 2. Confirm operating pressure

Pressure directly affects droplet size and drift risk. Set it deliberately, not by habit:

- Field spraying typically operates between 2–3 bar (30–45 psi).
- Lower pressure produces coarser droplets — better for reducing drift.
- Higher pressure produces finer droplets — better coverage, but higher drift risk.

Always match your pressure to the product label requirements and the prevailing drift risk conditions on the day.

### Step 3. Measure actual nozzle output

Use clean water for this test to avoid contamination and get a true baseline reading:

- Run the sprayer at your intended operating pressure.
- Collect the output from one nozzle for exactly 1 minute into a measuring jug.
- Record the volume in millilitres (mL).
- Repeat the test across several nozzles along the full length of the boom.

**Acceptance threshold**

All nozzles should be within 10% of each other. Anything outside this range will cause uneven application across the boom — the root cause of striping and patch failure.

### Step 4. Calculate your water rate (L/ha)

Once you have a confirmed nozzle output figure, use the standard formula to calculate your actual water rate:

**The water rate formula**

**Water rate (L/ha) = (600 × Nozzle output L/min) ÷ (Speed km/h × Nozzle spacing m)**

#### Worked example

| **Nozzle output** | 0.8 L/min |
| --- | --- |
| **Travel speed** | 8 km/h |
| **Nozzle spacing** | 0.5 m |
| **Result** | (600 × 0.8) ÷ (8 × 0.5) = 120 L/ha |

If your result doesn't match your target rate, adjust travel speed or operating pressure — then re-measure to confirm.

## Quick Reference Summary

**Pre-spray checklist**

- Nozzles matched — same type and size across the full boom
- No nozzle varies more than ±10% from rated output
- Pressure set to match product label and conditions
- Water rate calculated and confirmed against target
- Boom height and speed locked in before entering the paddock

**How Highlands Ag Solutions can help**

- Spray rig calibration reviews and on-farm support
- Herbicide and pesticide program planning
- Resistance management and product selection advice
- Chemical use records and compliance guidance

**[Book a free on-farm consultation →](https://www.highlandsagsolutions.com.au/contact-highlands-ag-solutions)**

[View full post](https://www.highlandsagsolutions.com.au/the-farm-shed/calibrating-your-spray-rig)

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