Three ways a label gives the rate
Colorado State University Extension, in its fact sheet on mixing small spray quantities, notes that labels give mixing directions in one of two general ways. One is an amount per volume of water, a concentration. The other is an amount per area. Many garden products also give a ratio, which is just a concentration written differently. The calculator handles all three:
ratio 1 : N: product = 1,000 ÷ N mL for every litre of water
per m²: product = label mL ÷ label m² × your m² · spray = your m² × ( test litres ÷ test m² )
Worked examples
- "10 mL per litre" in a 5 L pump sprayer: 10 × 5 = 50 mL, topped up to 5 L with water.
- A ratio of 1:50: one part product to 50 parts water is 1,000 ÷ 50 = 20 mL per litre. In a 5 L sprayer that is 100 mL.
- A watering-can rate in a smaller can: Seasol's own advice for its hose-on pack is 200 mL of solution per 9 L watering can for established gardens and vegetables. That is 22 mL per litre, or 111 mL in a 5 L can.
- A rate per area: say a lawn product says 20 mL per 10 m², and your lawn is 50 m², so you need 100 mL of product. You sprayed 2 L of plain water over 20 m² in the test, so your sprayer puts 0.1 L on each square metre. The lawn needs 5 L of spray, one 5 L sprayer fill with 100 mL of product.
Why rates per area need a sprayer test
A rate per area fixes how much product lands on each square metre, not how strong the mix is. Two people with the same sprayer can put very different amounts of liquid on the same patch, depending on nozzle, pressure and walking speed. Colorado State's method is simple:
- Put a known amount of plain water in the sprayer.
- Spray it the same way you will spray the product, at the same pace.
- Measure the area you covered.
Enter the result in the calculator. It works out how much spray your area takes, how much product goes into it, and how many times you will fill the sprayer. Mix only enough for the area, because leftover spray is a disposal problem.
Measuring small amounts
Colorado State warns that a common teaspoon holds anywhere from 4 to 10 mL. That is enough error to double a dose. Use a graduated measuring cup or a syringe marked in millilitres (1 cc is 1 mL). Keep it only for garden chemicals, labelled, and never use it in the kitchen. For doses under about 10 mL, a syringe is the only practical way to be accurate.
| Label rate | Per litre | 5 L sprayer | 9 L can |
|---|---|---|---|
| 5 mL per litre | 5 mL | 25 mL | 45 mL |
| 10 mL per litre | 10 mL | 50 mL | 90 mL |
| 1 part to 100 | 10 mL | 50 mL | 90 mL |
| 1 part to 50 | 20 mL | 100 mL | 180 mL |
| 1 part to 20 | 50 mL | 250 mL | 450 mL |
The label is the law
In Australia, pesticide labels, including home-garden weed killers and insect sprays, are approved by the national regulator, the APVMA. Their directions are not suggestions. In NSW, for example, the EPA states that everyone using a pesticide must read the label and follow its directions. Using one in a way the label does not allow is an offence under the Pesticides Act 1999. So:
- Use the rate for your exact use, and never "a bit stronger to be sure". More concentrate does not always mean faster results, and it can damage plants or soil.
- Don't mix two products together unless both labels say you can.
- Follow the label's safety directions for gloves, eye protection and keeping people and pets off the area.
- Rinse the sprayer as the label directs, and never let spray or washings run into drains or waterways.
Liquid fertilisers and seaweed tonics are not pesticides, but the same arithmetic applies. The fertiliser calculator works out granular feeds per square metre.
Mixing questions
How do I work out how much concentrate to put in my sprayer?
Divide the label's millilitres by its litres to get mL per litre, then multiply by the litres of water in your sprayer. A label rate of 20 mL per 2 L is 10 mL per litre, so a 5 L sprayer needs 50 mL.
What does a ratio like 1:50 mean?
One part of product to 50 parts of water: 1,000 ÷ 50 = 20 mL for every litre of water. In a 9 L watering can that is 180 mL.
How much Seasol goes in a 9 litre watering can?
For the hose-on pack, Seasol gives 80 mL per 9 L for seedlings and new plants, 200 mL for established gardens, vegetables and lawns, and 400 mL for large or stressed trees. Concentrate bottles have their own rates, so check the label on yours.
Can I use a kitchen teaspoon to measure?
No. Colorado State University Extension notes that a common teaspoon holds 4–10 mL. Use a graduated measure or a syringe marked in mL, and keep it only for garden chemicals.
Sources and method
- Colorado State University Extension, The preparation of small spray quantities of pesticides, fact sheet 7.615 (revised October 2020) – rates per volume vs per area, the sprayer test, teaspoon variation, measuring tools.
- Seasol, Dilution rates for 9 L watering cans – hose-on pack rates for Seasol and PowerFeed.
- NSW Environment Protection Authority, Pesticide use in NSW – reading and following the label, offences under the Pesticides Act 1999.
- Australian Pesticides and Veterinary Medicines Authority, Understanding pesticide labels.
Written by DueRiva · Last reviewed 24 September 2026 · Report an error