Direct comparison
Proportion vs Percentage: Differences and Usage
Proportion vs percentage: a proportion is a 0-1 fraction, a percentage is the same value per hundred. Conversion, reporting rules and when to use each.
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How do Proportion, Percentage compare side by side?
The table below compares Proportion, Percentage across 11 procurement-relevant dimensions, from what it expresses through source.
Side-by-side comparison
| Dimension | Proportion | Percentage |
|---|---|---|
| What it expresses | A part divided by the whole, written as a number. | The same part-of-whole value expressed per hundred; in written text the symbol % generally means 'parts per hundred' (BIPM SI Brochure 5.4.7). |
| Usual scale | 0 to 1 (0 = none of the whole, 1 = all of it). | 0 to 100 (0 % = none of the whole, 100 % = all of it). |
| Relationship | Multiply by 100 to get the percentage: 0.25 becomes 25 %. | Divide by 100 to get the proportion: 25 % becomes 0.25. NIST SP 811 7.10.2 accepts % as the symbol for the number 0.01. |
| Symbol | None: it is a plain number. | The symbol %. Both NIST and BIPM say the symbol should be used rather than the name 'percent' or 'per cent'. |
| Spacing in SI style | Not applicable. | A space separates the number and the symbol (10 %), per NIST SP 811 and BIPM 5.4.7. Some journal styles differ, so follow the target journal. |
| Qualifiers such as 'by mass' | Name the quantity instead: 'the mass fraction is 0.10' (NIST). | Avoid 'percentage by mass', 'percentage by volume', '% (m/m)'; write 'the mass fraction is 10 %' (NIST, BIPM). |
| Other meaning of the word | In maths teaching, a proportion can also mean an equality of two ratios. In statistics it means the part-of-whole value above. | Only the per-hundred meaning. |
| Comparing two values | Subtract: 0.25 minus 0.20 is a difference of 0.05 (the writer's own arithmetic). | NIST flags 'differ by 0.05 %' as incorrect for relative differences and asks for a defined quantity, such as R1 = R2(1 + 0.05 %) or Delta = (R1 - R2)/R2. |
| Worked example (illustrative arithmetic) | 30 of 120 samples pass: 30 / 120 = 0.25. | The same result reported to readers: 25 % of samples pass. |
| When to pick each | Formulas, test statistics and software input where a 0-1 value is required. | Text, tables and figures meant for readers, where a share per hundred is easiest to read. |
| Source | NIST SP 811 section 7.10.2 (read 2026-10-29). | BIPM SI Brochure, 9th edition, section 5.4.7 (read 2026-10-29). |
Common questions
Common questions about Proportion vs Percentage
What is the difference between proportion and percentage?
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They express the same part-of-whole value on different scales. A proportion is a number from 0 to 1; a percentage is that number expressed per hundred, so a proportion of 0.25 is 25 %. NIST SP 811 section 7.10.2 accepts the symbol % for the number 0.01.
How do you convert a proportion to a percentage?
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Multiply by 100 and add the % symbol: 0.25 becomes 25 %. To go back, divide by 100.
Should I write 'percent' or use the % symbol?
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The BIPM SI Brochure and NIST SP 811 both say the symbol % should be used rather than the name 'percent' or 'per cent', with a space between number and symbol. Check your target journal, because some styles differ.
Can I write 'percentage by mass' in a paper?
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SI guidance says not to. NIST and BIPM advise stating the quantity itself, for example 'the mass fraction is 10 %' or 'the mass fraction is 0.10'.
Going deeper
