mg/kg to PPM Calculator
Here is a conversion that surprises people with how simple it is: on a mass basis, mg/kg and PPM are the same number. 45 mg/kg of lead in soil is 45 PPM. No math, just a change of label — but the basis has to be mass.
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mg/kg to PPM Calculator
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Here is a conversion that surprises people with how simple it is: on a mass basis, mg/kg and PPM are the same number. 45 mg/kg of lead in soil is 45 PPM. No math, just a change of label — but the basis has to be mass.
How to use this calculator
- Enter the mg/kg value.
- That number is your PPM (mass basis).
- Confirm the basis is mass/mass.
The formula
1 PPM (mass) = 1 part per 10⁶ parts = 1 mg per 10⁶ mg = 1 mg/kg. Identical by definition.
What the units mean
mg/kg — milligrams per kilogram, a mass-basis concentration. Numerically identical to PPM on a mass basis; the unit soil and food laboratories report in.
PPM (parts per million) — one part of solute per million parts of the total mixture. The workhorse unit for trace concentrations in water, air, and food.
Worked example
A soil test shows 120 mg/kg lead → 120 PPM (mass basis). Compare directly with the 400 PPM screening level.
Quick reference
| mg/kg | PPM |
|---|---|
| 1 | 1 |
| 10 | 10 |
| 50 | 50 |
| 100 | 100 |
| 500 | 500 |
Numerically identical on a mass basis.
Where you will actually use this
Soil tests, food contaminant reports, and solid-sample analyses quote mg/kg. Everyone else says PPM. Now they match.
- Soil contamination reports
- Food heavy-metal testing
- Solid waste analysis
- Fertilizer labels
Mistakes that give wrong answers
- Applying this to liquids without checking basis
- Assuming mg/L = mg/kg (that needs density)
Key takeaways
- Formula: PPM = mg/kg (mass basis, numerically identical)
- Remember: Numerically identical on a mass basis.
- Watch out for: Applying this to liquids without checking basis
- Next step: run your own numbers in the calculator above, then verify with a measurement — calculated values are only as good as the inputs.
Frequently asked questions
Is mg/kg the same as PPM?
Yes, on a mass basis — numerically identical.
What is 50 mg/kg in PPM?
50 PPM.
Does this work for water samples?
Only if you convert via density; water reports usually use mg/L instead.