About the Percent Solution Calculator
This percent solution calculator handles the three ways percentage concentration is written on reagent bottles and in protocols. Weight/volume (% w/v) means grams of solute per 100 mL of final solution, weight/weight (% w/w) means grams per 100 g of solution, and volume/volume (% v/v) means millilitres per 100 mL. Choose the type, then either enter the percentage you want to make and the final amount, or enter what you dissolved to find the resulting percentage.
It is aimed at students and lab staff making up things like 0.9% saline, 2% agarose, 10% SDS, 70% ethanol or 5% acetic acid. For w/v solutions you can also enter the molar mass to see the equivalent molarity and g/L, which helps when one protocol uses percent and another uses molar units.
For w/v and v/v solutions, the solute is dissolved and then topped up to the final volume — not added to that volume of solvent. For v/v mixtures the solvent volume shown is the simple difference and ignores volume contraction (ethanol and water, for example, shrink by a few percent when mixed).
How to use the percent solution calculator
- 1Choose w/v, w/w or v/v to match your protocol.
- 2Choose whether you need the solute amount or the resulting percentage.
- 3Enter the target percentage (or the solute you used) and the final amount.
- 4For w/v, optionally add the molar mass to see molarity.
- 5Weigh or measure the solute, then make up to the final amount.
Formula and method
All three percentages are a part-over-whole ratio multiplied by 100; they differ only in whether mass or volume is used for each part. To make a solution, rearrange: solute = percentage ÷ 100 × final amount. For w/w the remaining mass is solvent, so solvent = total − solute.
Because 1% w/v is 1 g per 100 mL, it equals 10 g/L. Dividing g/L by the molar mass gives molarity, so a 0.9% w/v NaCl solution is 9 g/L ÷ 58.44 g/mol ≈ 0.154 M. Volumes are always the final solution volume, not the volume of solvent added.
- w
- Mass (g)
- v
- Volume (mL)
- M
- Molarity = g/L ÷ molar mass
Worked examples
500 mL of 5% w/v sodium chloride
5% w/v is 5 g per 100 mL, so 500 mL needs 5 ÷ 100 × 500 = 25 g of NaCl, dissolved and topped up to 500 mL. That is 50 g/L, or 50 ÷ 58.44 ≈ 0.856 M.
250 g of a 10% w/w solution
A 10% w/w solution weighing 250 g contains 25 g of solute, so you mix 25 g of solute with 225 g of solvent.
Percentage of 35 mL ethanol in 250 mL
35 mL of ethanol made up to 250 mL is 35 ÷ 250 × 100 = 14% v/v. About 215 mL of water is needed, slightly more in practice because ethanol–water mixtures contract.
Frequently asked questions
How do you make a 10% w/v solution?+
Weigh 10 g of solute for every 100 mL of final volume, dissolve it in less than the final volume of solvent, then top up to the mark. For 1 L you would dissolve 100 g and make up to 1000 mL.
What is the difference between w/v and w/w?+
w/v divides the solute mass by the solution volume (g per 100 mL), while w/w divides by the solution mass (g per 100 g). They are only equal when the solution density is exactly 1 g/mL.
How do I make 70% ethanol from 95% ethanol?+
That is a dilution rather than a fresh percent solution: use C₁V₁ = C₂V₂. For 100 mL of 70% you need 70 × 100 ÷ 95 ≈ 73.7 mL of 95% ethanol topped up to 100 mL with water.
How do I convert percent w/v to molarity?+
Multiply the percentage by 10 to get g/L, then divide by the molar mass. For example, 2% w/v glucose is 20 g/L ÷ 180.16 g/mol ≈ 0.111 M.
Why add solvent up to the volume instead of adding a set volume?+
Dissolving a solute changes the total volume, so adding 100 mL of water to 10 g of salt does not give exactly 100 mL of solution. Making up to the mark guarantees the stated percentage.