Why the conversion factor is 10
A value of p% w/v means p grams of the named ingredient in 100 mL of final solution. Since 1 g equals 1,000 mg, the concentration is p × 1,000 ÷ 100 mg/mL.
% w/v = mg/mL ÷ 10
For example, 2.5% w/v means 2.5 g per 100 mL. That is 2,500 mg per 100 mL, or 25 mg/mL. In reverse, 25 mg/mL divided by 10 gives 2.5% w/v.
No liquid density is used in this conversion. The volume basis is already stated in the definition of % w/v; there is no assumption that every milliliter of the liquid weighs one gram.
Three percentages with different meanings
| Basis | What 1% means | Use this tool? |
|---|---|---|
| w/v or m/v | 1 g ingredient per 100 mL final solution | Yes, when confirmed |
| w/w or m/m | 1 g ingredient per 100 g mixture | No; mass basis |
| v/v | 1 mL ingredient per 100 mL final mixture | No; volume basis |
The FDA's explanation of concentration formats separates these mass and volume expressions. A bare “1%” does not identify which one applies.
Look for “w/v,” “m/v,” “g per 100 mL,” or an equivalent explicit statement in the source information. If the basis is missing, ask the product supplier or the person who provided the value. For a medicine label, confirm unclear information with a pharmacist or clinician.
A few reference points
| % w/v | g per 100 mL | mg/mL |
|---|---|---|
| 0.1% | 0.1 g | 1 mg/mL |
| 0.9% | 0.9 g | 9 mg/mL |
| 1% | 1 g | 10 mg/mL |
| 2.5% | 2.5 g | 25 mg/mL |
These rows are unit examples, not suggested products, concentrations or amounts to use. Enter the percentage number as written: for 0.9%, use 0.9.
Concentration is not a volume to use
A concentration describes the amount of an ingredient in a unit of solution. It does not determine a dose, an application amount or a schedule. This page only rewrites a concentration you already know.
When you have a separately specified mass and a confirmed concentration, the main mg to mL converter can do the mass-to-volume arithmetic. Keep the units visible and use the concentration of the actual material.
Use the final solution volume
“Per 100 mL” describes the completed solution. It is not automatically the amount of solvent added. A preparation's final volume and the starting solvent volume can differ; this calculator does not supply mixing or preparation instructions.
If the source already gives a ratio such as mg per 5 mL, use the concentration label converter directly. Converting that ratio to a percentage first only adds an unnecessary step.
Rounding and limits
The result displays six significant figures with a leading zero for values below one. Calculations use the entered value before display rounding. A zero entry gives a zero concentration; it does not provide a usable divisor for a mass-to-volume conversion.
Because w/v compares different types of quantity, it is not the same as a mass fraction limited to 100%. This tool does not establish whether a concentration is physically achievable or suitable for a particular substance.
Method and sources
FDA: Strength Conversion in Drug Listing describes w/v, w/w and v/v expressions. BIPM: SI prefixes defines milli- and the gram-to-milligram factor. Calculations stay in your browser and are not saved.
Reviewed September 15, 2026. Send corrections to contact@mgtoml.app.