Ratio & proportion tools
Ratio to Percentage Calculator
A ratio does not have one percentage. It has one percentage per question you might be asking, and this tool shows both, clearly labelled.
Exact result
75%
A compared with B — how big the first part is relative to the second
Share of the whole
Each part measured against the total of 7 parts.
- first part share
- 42.86%
- second part share
- 57.14%
Both answers, side by side
- Compared with B: first ÷ second × 100 = 75%.
- Compared with A: second ÷ first × 100 = 133.33%.
- Share of the whole: 42.86% and 57.14%.
Interpretation comes before conversion
The chain from a ratio to a percentage is mechanical — ratio → fraction → decimal → percentage — but the first link is a choice, not a calculation. Take 3:4. It can answer two different questions, and each gives a different fraction to start from.
3:4 — two questions, two answers
Part to part. How big is A compared with B? 3 / 4 = 0.75 = 75%.
Part to whole. What share of everything is A? 3 / (3 + 4) = 3 / 7 ≈ 42.857%.
These do not contradict each other. 75% and 42.857% answer different questions about the same ratio.
The tell is the denominator. Part-to-part divides by the other part; part-to-whole divides by the sum of all parts. Every argument about a "wrong" ratio percentage is, in practice, an argument about which denominator was intended.
The two procedures
Part to part: a:b → a/b → decimal → percentage
- Write the first part over the second: 3:4 → 3/4.
- Divide: 3 ÷ 4 = 0.75.
- Multiply by 100: 75%.
- Read it as: A is 75% of B. Above 100% is normal here — 4:3 gives 133.33%.
Part to whole: a:b → a/(a+b) → decimal → percentage of total
- Add all parts for the total: 3 + 4 = 7.
- Write the part over the total: 3/7.
- Divide: 3 ÷ 7 = 0.428571… (exactly 3/7).
- Multiply by 100: ≈ 42.857%. This reading can never exceed 100%.
Four representations, side by side
The table below never lists a percentage without saying what it represents, because the same ratio appears in more than one row with different values.
| Relationship | Ratio | Fraction | Decimal | Percentage |
|---|---|---|---|---|
| A relative to B | 3:4 | 3/4 | 0.75 | 75% |
| A as a share of the whole | 3:4 | 3/7 | 0.428571… | ≈ 42.857% |
| B as a share of the whole | 3:4 | 4/7 | 0.571428… | ≈ 57.143% |
| B relative to A | 3:4 | 4/3 | 1.333… | ≈ 133.333% |
| A relative to B | 1:4 | 1/4 | 0.25 | 25% |
| A as a share of the whole | 1:4 | 1/5 | 0.2 | 20% |
| A relative to B | 1:1 | 1/1 | 1 | 100% |
| A as a share of the whole | 1:1 | 1/2 | 0.5 | 50% |
| A as a share of the whole | 2:3:5 | 2/10 | 0.2 | 20% |
| C as a share of the whole | 2:3:5 | 5/10 | 0.5 | 50% |
1:4 is the clean illustration: 25% and 20% are both correct and mean different things.
Part-to-whole percentages across all parts must total 100% — 42.857% + 57.143% for 3:4, and 20% + 30% + 50% for 2:3:5. Part-to-part percentages have no such rule. That is the fastest way to tell which reading a set of figures belongs to.
Reverse-checking the result
Each direction has an inverse that returns you to the ratio, and the inverses differ.
From 42.857% back to 3:4
- It is a share of the whole, so it is p/100 of the total: 42.857/100 ≈ 3/7.
- The remainder of the whole is 4/7.
- Write the two over the same denominator and keep the numerators: 3:4 ✓
From 75% back to 3:4
- It is a part-to-part figure, so it is A/B: 75/100 = 3/4.
- Numerator to denominator: 3:4 ✓
- Note it does not reduce to 3:1 — the denominator here is the other part, not the total.
Going the other way from an arbitrary percentage — deciding whether 25% means 1:4 or 1:3 — is its own decision, handled on percentage to ratio.
Exactness
3/7 has no finite decimal. SnapRatios keeps it as the exact fraction and rounds only for display, so the shares still reconcile to 100% instead of drifting to 99.99% — the methodology covers the arithmetic.