Ratio & proportion tools
1:1 Ratio Calculator
Equal parts — the one ratio where the arithmetic is trivial and the wording still trips people up.
1:1
Two parts · one half each · 50% / 50%
Exact result
50 units · 50 units
50% : 50% · 2 total parts · 1 part = 50 units
- Total parts
- 2
- Simplest form
- 1 : 1
- One part
- 50 units
Know one side instead?
Enter one measured amount to scale the whole ratio.
Working
- Add the parts: 2 total parts.
- One part = 100 ÷ 2 = 50 units.
- Multiply one part by each ratio part: 50 and 50.
Equivalent 1:1 ratios
- 1 : 1
- 2 : 2
- 3 : 3
- 4 : 4
- 5 : 5
- 6 : 6
Equal parts, two halves
1:1 says the two quantities are the same size. Divide a total between them and each side receives one half — not because 1:1 contains a 2, but because the parts add to 2 and one part is the total divided by that sum.
100 divided 1:1
- Total parts: 1 + 1 = 2.
- One part: 100 ÷ 2 = 50.
- Shares: 1 × 50 = 50 and 1 × 50 = 50.
Why 1:1 is not “100% of the total”
The 1 in 1:1 is a count of parts, not a share of the whole. Each 1 becomes 1/2 of the total once you add the parts together. Reading either 1 as “one whole” is the denominator mistake: it silently swaps the part-to-part comparison for a part-to-whole one.
| Statement | Compares | First quantity is |
|---|---|---|
| 1:1 | Part with part | 1/2 of the total (50%) |
| 1 in 1 | Part with whole | The entire total (100%) |
| 1:1 reversed (1:1) | Part with part | Unchanged — 50% |
Only in a part-to-whole reading does a 1 mean the whole thing.
Equality is a symmetry, not just a number
Every other ratio changes meaning when you swap the order: 3:2 and 2:3 are different. 1:1 is the single two-part ratio that is its own reverse, which is why it is the safe default whenever the order of your two labels is uncertain or irrelevant.
It is also the fixed point of scaling. Multiply both parts by anything — 7:7, 250:250, 0.5:0.5 — and the simplest form is still 1:1. If a calculation that should have preserved equality returns anything else, the two parts were not equal to begin with.
Where the equality itself is the point
Three cases
Two people sharing a £84 bill equally: one part is £42, so £42 each.
A 1:1 simple syrup: 300 g sugar and 300 g water, measured in the same unit.
A 1:1 image crop: width equals height, so 1080 px becomes 1080 × 1080.