Enter the amount of substance in milligrams and the mass in kilograms into the calculator to determine the concentration in milligrams per kilogram (mg/kg).
Mg Per Kg Formula
Milligrams per kilogram (mg/kg) is a mass-based concentration unit. It tells you how many milligrams of a substance are present in each kilogram of total material. This format is commonly used for lab results, contaminants, nutrients, additives, and body-mass-normalized measurements.
C = mg / kg
Where:
- C = concentration in mg/kg
- mg = amount of substance in milligrams
- kg = total mass in kilograms
If you know any two values, you can solve for the third:
mg = C * kg
kg = mg / C
How to Calculate mg/kg
- Determine the amount of the substance.
- Convert that amount to milligrams if needed.
- Determine the total sample or body mass.
- Convert that mass to kilograms.
- Divide milligrams by kilograms to get the final mg/kg value.
When calculating manually, keep the numerator and denominator as mass units. If your input is in grams or pounds, convert before solving to avoid scaling errors.
Examples
Example 1: A sample contains 500 mg of a substance and has a total mass of 2 kg.
C = 500 / 2 = 250
The concentration is 250 mg/kg.
Example 2: A target concentration is 40 mg/kg and the batch mass is 3.5 kg.
mg = 40 * 3.5 = 140
You need 140 mg of the substance.
Example 3: A sample contains 90 mg and the measured concentration is 30 mg/kg.
kg = 90 / 30 = 3
The total mass is 3 kg.
What mg/kg Means in Practice
A value of 1 mg/kg means there is one milligram of substance for every one kilogram of material. Because it is a ratio, the same formula works whether the kilogram refers to a soil sample, food product, feed, chemical mixture, or body weight.
In toxicology and medicine, mg/kg often describes dose per kilogram of body weight. In chemistry and environmental testing, it usually describes concentration within a sample. The math is identical, but the meaning depends on what the kilogram represents.
Common Conversions and Equivalents
These relationships are useful when comparing mg/kg to other reporting units:
1 \text{ mg/kg} = 1 \text{ ppm}1 \text{ mg/kg} = 0.0001\%1\% = 10000 \text{ mg/kg}1 \text{ g/kg} = 1000 \text{ mg/kg}1 \text{ mg/g} = 1000 \text{ mg/kg}1 \text{ mg/lb} \approx 2.20462 \text{ mg/kg}| Unit | Meaning | Typical Use |
|---|---|---|
| mg/kg | milligrams per kilogram of mass | solids, body-weight dosing, mass-based concentration |
| ppm | parts per million | dilute mass-based reporting |
| mg/L | milligrams per liter of volume | liquids and solutions |
| % | parts per hundred | higher concentrations |
Where This Calculator Is Useful
- Environmental testing: soil, sediment, ash, compost, and waste analysis
- Food and feed: nutrient concentration, additive levels, and residue reporting
- Chemistry labs: reporting trace amounts in bulk samples
- Toxicology and medicine: dosage or exposure expressed per kilogram of body weight
- Manufacturing and quality control: checking low-level components in a larger batch
Tips for Accurate Results
- Use the mass of the substance, not its volume.
- Use the total sample mass for the denominator.
- Convert units before solving if values are entered in grams, pounds, or kilograms.
- Do not confuse mg/kg with mg/L; one is mass-per-mass and the other is mass-per-volume.
- If the kilogram value is very small, the mg/kg result will be much larger.
- The denominator must be greater than zero.
Frequently Asked Questions
Is mg/kg the same as ppm?
For mass-by-mass measurements, yes. The numerical value is the same, so 25 mg/kg is equal to 25 ppm.
How do I find milligrams from mg/kg?
Multiply the concentration by the total kilograms of material.
mg = C * kg
How do I find kilograms if I know mg and mg/kg?
Divide the milligrams by the concentration.
kg = mg / C
What does 250 mg/kg mean?
It means each kilogram of the material contains 250 milligrams of the substance being measured.
