The off-by-one, and why it costs you money
A label says 1:9. Most people reach for a 10 litre bucket and divide by 9. That gives 1.11 litres of concentrate. The right answer is 1 litre, because 1:9 is one part concentrate to nine parts water — ten parts all up, and the concentrate is one of them.
It is a small error at weak ratios and a real one at strong ratios, and the size of it is easy to remember: dividing by N instead of N + 1 makes the mix stronger by 1/N.
| Ratio | Right (per litre) | Divide-by-N (per litre) | How much too strong |
|---|---|---|---|
| 1:4 | 200 mL | 250 mL | 25% too strong |
| 1:10 | 90.9 mL | 100 mL | 10% too strong |
| 1:20 | 47.6 mL | 50 mL | 5% too strong |
| 1:50 | 19.6 mL | 20 mL | 2% too strong |
| 1:100 | 9.9 mL | 10 mL | 1% too strong |
At 1:100 nobody will ever notice. At 1:4 you are burning a quarter more product on every bucket, all day, for the life of the business. On a cleaning run that gets through a couple of drums a month, that is real money walking out the door.
Common ratios, done properly
| Ratio | Concentrate share | Per 1 litre | Per 10L bucket |
|---|---|---|---|
| 1:4 | 20% | 200 mL | 2 L |
| 1:9 | 10% | 100 mL | 1 L |
| 1:10 | 9.1% | 90.9 mL | 909 mL |
| 1:20 | 4.8% | 47.6 mL | 476 mL |
| 1:50 | 2.0% | 19.6 mL | 196 mL |
| 1:100 | 1.0% | 9.9 mL | 99 mL |
| 1:200 | 0.5% | 5.0 mL | 50 mL |
Note the difference between 1:9 and 1:10. They look almost the same on a label and they are not the same mix — 1:9 is a clean 10%, 1:10 is 9.1%. If a supplier changes the ratio on a reformulated product, that is the kind of change that goes straight past you.
Two worked examples
A 10 litre mop bucket at 1:9. 10 ÷ (9 + 1) = 1 litre of concentrate, 9 litres of water. Do it the wrong way and you tip in 1.11 litres — one extra litre for every nine buckets.
A 5 litre pump sprayer at 1:50. 5,000 mL ÷ 51 = 98 mL of concentrate and 4,902 mL of water. That is a measured 98, not "a decent glug", and the difference between 98 and 100 is nothing while the difference between 98 and 250 is a burnt lawn.
Mixing it without wrecking anything
- Water first, then concentrate. Adding concentrate to water is the safe order. Pouring water onto neat concentrate splashes it back at your face and hands, and with some chemicals the mixing reaction gives off heat.
- Use a measuring jug. Every time. A cap is not a measure, and a glug is not a number. Keep a marked jug per chemical so you are not measuring an acid in the jug you use for a neutral detergent.
- Never mix two chemicals together. Not in the bucket, not in the sprayer, not "just a bit of both to save time". Bleach with an acidic cleaner gives off chlorine gas. Bleach with ammonia gives off chloramine. People end up in hospital doing this in bathrooms every year.
- Read the safety data sheet, not just the front of the bottle. The SDS gives the PPE, the ventilation, the first aid and what it must not be stored next to. If you have staff, you need it on hand anyway.
- Label the bottle with the product name and the dilution. An unlabelled spray bottle in the back of a van is a hazard for whoever picks it up next.
Stronger is not better
Over-concentrating feels like insurance. It is not:
- It leaves residue. Too much detergent does not rinse out — it dries as a film that holds dirt, so the floor looks worse a week later and you get called back.
- It damages surfaces. Neat or near-neat alkaline cleaner will haze polished stone, strip a seal, dull vinyl and lift a coating. Those are repair bills, not touch-ups.
- It wastes product. These chemicals are formulated to work at the label rate. Doubling the dose does not double the result.
Under-concentrating fails the other way. The job takes twice the scrubbing, does not sanitise properly if that is the point of the product, and burns time — which costs more than the chemical you saved.
Weed killer and garden chemicals
The same arithmetic, with one important difference: for agricultural and veterinary chemicals registered in Australia, the label is a legal instruction, not a suggestion. Using a registered product at a rate other than the label rate, or for a use it is not registered for, is an offence. Follow the label.
Two practical notes. Many garden chemical labels give a rate directly in millilitres per litre rather than as a ratio — if it says 10 mL per litre, use that and skip the ratio maths. And mix only what you will use that day: diluted product does not keep, and leftover mix in a sprayer is a disposal problem, not a saving.
When the label is ambiguous
"1:10" and "1 in 10" are written as though they mean the same thing and they do not. A ratio of 1:10 is one part in eleven. "1 in 10" usually means one part of ten — a straight 10%. If a label is unclear, ring the manufacturer rather than guessing. On an expensive product or a delicate surface, that phone call is cheaper than the alternative.
Mixed and measured. Now bill the job properly.
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Try Yamate free → Free to try · no card · sign in with a link, no password to rememberDilution ratio FAQ
What does a 1:10 dilution ratio mean?
One part concentrate to ten parts water — eleven parts in total. So the concentrate is 1/11 of the mix, about 9.1%, which is 90.9 mL per litre or 909 mL in a 10 litre bucket. It is not one tenth.
How do I work out a dilution ratio?
Divide the total amount you want by N + 1, where N is the water side of the ratio. For 1:9 in a 10 litre bucket that is 10 ÷ 10 = 1 litre of concentrate and 9 litres of water. Dividing by N instead of N + 1 is the usual mistake.
How much concentrate for a 1:50 dilution in a 5 litre sprayer?
5,000 mL ÷ 51 = about 98 mL of concentrate, topped up with roughly 4,902 mL of water. Measure it in a jug rather than estimating.
Is 1:9 the same as 1:10?
No. 1:9 is one part in ten, a clean 10%. 1:10 is one part in eleven, about 9.1%. They look nearly identical on a label and they are different mixes.
Do I add the concentrate to the water or the water to the concentrate?
Concentrate into water, always. Pouring water onto neat concentrate can splash it back at you, and with some chemicals the mixing gives off heat. Part-fill with water, add the concentrate, then top up.
What happens if I make a cleaning solution too strong?
It leaves a residue that will not rinse out and attracts dirt, it can haze stone, strip seals and dull vinyl, and it burns through product for no extra cleaning. Stronger is not better — these chemicals are formulated to work at the label rate.
Can I mix two cleaning chemicals together?
No. Bleach with an acidic cleaner gives off chlorine gas, and bleach with ammonia gives off chloramine. Use one product at a time, rinse between them, and read the safety data sheet.
Other calculators you'll want
General information for Australian trades, and an estimate only — not tax, financial or legal advice. It is not engineering, building or design advice either: a calculator works out a quantity from the figures you enter, and anything that needs sign-off still needs your engineer, certifier or building surveyor. This is arithmetic against the ratio you enter. Always follow the manufacturer's own instructions and the product's safety data sheet — they set the correct rate, the personal protective equipment and the handling precautions for that specific product. For agricultural and veterinary chemicals registered in Australia, the label rate is a legal requirement. Never mix chemicals together.