1:10 is one part in eleven, not one in ten
A ratio names the concentrate against the water, so 1:10 is 1 part product to 10 parts water — 11 parts in the bottle. The strength is 1 ÷ 11 ≈ 9.1%, not 10%. This one-part gap is the single most common dilution mistake, and it grows as the ratio tightens: 1:3 is 25% strength, not 33%.
Ratio, total parts and real strength
| Ratio (conc:water) | Total parts | Strength | Per US gallon |
|---|---|---|---|
| 1:4 | 5 | 20% | 25.6 oz |
| 1:9 | 10 | 10.0% | 12.8 oz |
| 1:10 | 11 | 9.1% | 11.6 oz |
| 1:32 | 33 | 3.0% | 3.9 oz |
| 1:50 | 51 | 2.0% | 2.5 oz |
| 1:100 | 101 | 0.99% | 1.3 oz |
"Per US gallon" is 128 fl oz divided by total parts — that much concentrate topped up to one gallon. An Imperial gallon is 160 fl oz, so UK figures run about 25% higher.
When the label gives ounces, not a ratio
- "Use 4 oz per gallon" is not "4:1". It is a dose, not a ratio. 4 oz in 128 oz of finished spray works out near 1:31.
- Match strength to the job. Bleach at 1:10 (about 5,000 ppm) suits blood or heavy disinfection; 1:100 (about 500 ppm) covers everyday surfaces. Too weak fails to disinfect; too strong wastes product and fumes.
- Mix fresh. Diluted bleach loses potency within about 24 hours as the chlorine breaks down, so make only what you will use.
Common questions
Does 1:10 mean 10% strength?
No. 1:10 means 1 part concentrate plus 10 parts water, which is 11 parts total, so the concentrate is 1 in 11, about 9.1%. To get exactly 10% you need a 1:9 mix.
Is 1:10 the same as 1+9?
Not quite, and this is where people slip. Written strictly, 1:10 is 1 part concentrate to 10 parts water. The 1+9 notation means 1 part concentrate added to 9 parts water, which totals 10 parts. Some labels use them loosely, so check whether the second number is water alone or the finished total.
How many ounces of concentrate go in a gallon?
A US gallon is 128 fluid ounces. Divide 128 by the total number of parts to get ounces of concentrate per gallon. At 1:32 that is 128 divided by 33, roughly 3.9 oz of concentrate topped up to a gallon.
