Convert Parts per million to Per cent
1 part per million is 0.0001 %. One part per million is exactly 0.0001 per cent.
One part per million is 1.0000 × 10^-4 per cent. To convert parts per million to per cent, multiply by 1.0000 × 10^-4; to go the other way, divide by 1.0000 × 10^-4 or multiply by 10000. The relation is exact but the figure is not: it is a rounding of a number that does not terminate, and it follows from NIST SP 811 §7.10.3. One in a million.
Factor checked against the defining standard · How we check
- Parts per million × 1.0000 × 10^-4
1 * 0.00010 %
1 part per million in every concentration unit
| Unit | Value | Exact factor |
|---|---|---|
| per cent | 0.0001 % | × 0.0001 |
| per mille | 0.001 ‰ | × 0.001 |
| parts per million (as entered) | 1 ppm | — |
| parts per billion | 1,000 ppb | × 1,000 |
| parts per trillion | 1,000,000 ppt | × 1,000,000 |
Factors are entered by hand from NIST SP 811 §7.10.3 rather than derived from a units library, so the ones that terminate are exact rather than rounded.
How do you convert parts per million to per cent? The converter and the working
- 1.Take the measurement in parts per million.
- 2.Multiply by 1.0000 × 10^-4 — that is how many per cent fit in one part per million.
- 3.To go back the other way, divide by 1.0000 × 10^-4, or multiply by 10000.
Worked example: 25 parts per million to per cent
- Formula
- ppm × 1.0000 × 10^-4 = %
- Arithmetic
- 25 × 1.0000 × 10^-4 = 0.0025 %
- Answer
- 25 ppm = 0.0025 %
The factor is rounded for display; the figure above is computed from the full value.
Parts per million to per cent conversion table
| Parts per million | Per cent |
|---|---|
| 1 ppm | 0.0001 % |
| 2 ppm | 0.0002 % |
| 3 ppm | 0.0003 % |
| 4 ppm | 0.0004 % |
| 5 ppm | 0.0005 % |
| 6 ppm | 0.0006 % |
| 7 ppm | 0.0007 % |
| 8 ppm | 0.0008 % |
| 9 ppm | 0.0009 % |
| 10 ppm | 0.001 % |
| 12 ppm | 0.0012 % |
| 15 ppm | 0.0015 % |
| 20 ppm | 0.002 % |
| 25 ppm | 0.0025 % |
| 50 ppm | 0.01 % |
| 100 ppm | 0.01 % |
| 200 ppm | 0.02 % |
| 300 ppm | 0.03 % |
| 500 ppm | 0.05 % |
| 1000 ppm | 0.1 % |
| 2000 ppm | 0.2 % |
| 5000 ppm | 0.5 % |
| 10000 ppm | 1 % |
1% is 10,000 ppm, and the factor catches people out in both directions
Per cent is parts per hundred and ppm is parts per million, so the step between them is 10,000 rather than 1,000 — one decimal place further than the eye expects. In water, 1 ppm is 1 milligram per liter, because a liter of water weighs a kilogram; that identity is why laboratory results and legal limits move between mg/L and ppm without conversion, and why 0.05% of chlorine is 500 ppm.
NIST Special Publication 811 — Guide for the Use of the International System of Units
What is a part per million?
One in a million. The working unit of drinking-water limits, CO₂ in air and dissolved solids — 1 ppm is 1 mg per liter of water, since a liter weighs a kilogram.
What is a per cent?
Parts per hundred. One per cent is 10,000 ppm, which is the conversion people reach for when a water report and a lab result are in different units.
How many per cent are in a part per million?
One part per million is 1.0000 × 10^-4 per cent. Going the other way, one per cent is 10000 parts per million. Both figures come from the same defined relation rather than from a measurement, which is why they are the same today as they were in 1959.
Every concentration unit here
The whole group — 5 units with their symbols and the size of each one in part per millions — is on the conversion index, along with every pair it makes. The table above already gives each of them relative to a part per million.
Source: NIST SP 811 §7.10.3 — why ppm, ppb and ppt should be avoided and what they mean
Cite this page
- APA
- Rule Calculator. (2026). Convert Parts per million to per cent. Rule Calculator. https://rulecalculators.com/convert/ppm-to-percent
- MLA
- "Convert Parts per million to per cent." Rule Calculator, August 16, 2026, https://rulecalculators.com/convert/ppm-to-percent.
- Chicago
- Rule Calculator. "Convert Parts per million to per cent." Rule Calculator. Last reviewed August 16, 2026. https://rulecalculators.com/convert/ppm-to-percent.
The date is when the figures on this page were last checked against their source, not the day you opened it. Add your own access date if your style needs one.
Questions people actually ask
- How many per cent are in a part per million?
- 1.0000 × 10^-4. Parts per hundred. One per cent is 10,000 ppm, which is the conversion people reach for when a water report and a lab result are in different units.
- How do I convert per cent back to parts per million?
- Divide by 1.0000 × 10^-4, or multiply by 10000 — they are the same operation.
Other concentration conversions
Per cent to parts per million — the same conversion the other way.