What this calculator does
Percent solution, when expressed as % weight/volume (% w/v), states how many grams of solute are dissolved in every 100 millilitres of solution. It is one of several ways chemistry and pharmacy express concentration as a percentage, and it is easy to confuse with % w/w (weight of solute per weight of total solution), which uses mass throughout instead of mixing mass and volume.
Because % w/v mixes units of mass and volume, it is not interchangeable with a true mass fraction unless the solution's density happens to be exactly 1 g/mL. It remains the standard way many pharmaceutical, biological and cleaning-product concentrations are labelled, precisely because volume is what gets measured out in practice.
The formula
Divide the mass of solute in grams by the volume of the solution in millilitres, then multiply by 100 to express it as a percentage. The same figure is also shown in grams per litre and milligrams per millilitre, which are the same ratio expressed at different scales.
| Term | Meaning |
|---|---|
| % w/v | Weight-per-volume percent: (mass of solute in g ÷ volume of solution in mL) × 100. |
| Solute | The substance being dissolved, whose mass is measured before it is made up to volume. |
| g/L | The same concentration expressed in grams per litre, numerically ten times the % w/v figure. |
The inputs explained
| Field | What to enter |
|---|---|
| Mass of solute (g) | The mass of solute dissolved, weighed out before the solution is made up to its final volume. |
| Volume of solution (mL) | The total volume of the finished solution, not just the volume of solvent added. |
When to use it
Preparing a lab reagent from a recipe
Many standard reagent recipes are given as a % w/v figure; this calculator checks that a prepared batch, or a scaled-up or scaled-down version of it, matches the intended concentration.
Reading a pharmaceutical or cleaning product label
Concentrations on many liquid product labels, from saline solutions to cleaning concentrates, are given as % w/v; converting to g/L or mg/mL makes it easier to compare against a recipe or dosing instruction expressed in those units.
Scaling a solution up or down
Working out the mass of solute needed for a different final volume, at the same % w/v strength, uses this same relationship rearranged for mass instead of percentage.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How percent solution changes with the mass of solute dissolved
A fixed 100 mL of solution, made up with a range of solute masses.
| Mass of solute | Percent solution (% w/v) | Concentration |
|---|---|---|
| 1 g | 1.000% | 10.00 g/L |
| 5 g | 5.000% | 50.00 g/L |
| 10 g | 10.000% | 100.00 g/L |
| 20 g | 20.000% | 200.00 g/L |
| 50 g | 50.000% | 500.00 g/L |
Questions
Is % w/v the same as % w/w?
No. % w/v is mass of solute per volume of solution (grams per 100 mL); % w/w is mass of solute per mass of solution (grams per 100 g). The two only give the same number if the solution's density is exactly 1 g/mL, which is rarely exact except for very dilute aqueous solutions.
Does % w/v depend on temperature?
Slightly, because the volume of a liquid can change a little with temperature, which shifts the volume the mass is divided by. In practice this effect is small for typical lab and household solutions and is usually ignored.
How do I convert % w/v to molarity?
Convert the % w/v figure to g/L (multiply by 10), then divide by the solute's molar mass to get mol/L. The molarity calculator performs that second step directly from a mass and volume.
What does a % w/v of, say, 0.9% mean in practice?
It means 0.9 g of solute are dissolved in every 100 mL of solution, which is the definition of normal saline (0.9% sodium chloride in water), a concentration chosen because it is isotonic with human blood plasma.
To convert a mass-based concentration into molarity instead, see the molarity calculator. For the related mass/mass percentage figure, see the mass percent concentration calculator.