Concentration Percent Calculator
Percent w/v, grams per liter, and mg per mL from solute mass and volume.
What it does
Percent concentration on lab and medical labels almost always means mass per volume: grams of solute sitting in each 100 mL of finished solution. A 2% salt solution therefore holds 2 g per 100 mL, or 20 g per liter. The tool above converts any solute and volume pair into that language plus g/L and mg/mL.
The default dissolves 5 g in 250 mL. Dividing gives 0.02, times 100 is 2% w/v. The same pair scales to 20 g per liter and 20 mg per mL, since milliliters and liters differ by exactly 1000. Those three readings describe one solution three ways.
Medicine runs on this unit. Physiological saline reads 0.9% because each 100 mL carries 0.9 g of salt, and blood glucose near 100 mg per dL is the same idea in smaller print. Chemistry texts frame it as a mixed mass volume ratio for settings where weighing is easier than counting moles.
The classic slip is topping up wrong: dissolving 5 g in 250 mL of water is not a 250 mL solution, because the solute adds its own volume. Pros dissolve first, then add solvent to the final mark in a volumetric flask. Home prep without that step still works for rough jobs but never for dosing.
How to use
- Weigh the solute in grams.
- Measure the final solution volume in mL.
- Type both values into the tool.
- Read percent w/v first for labels.
- Use g/L or mg/mL when scaling batches.
Formula
- % w/v
- Grams of solute per 100 mL of finished solution.
- g/L
- Grams per liter, percent times 10.
- mg/mL
- Milligrams per milliliter, same digits as g/L.
Volume means finished solution at the mark, after the solute dissolves. For dilute water work the added volume error is tiny; for syrups and brines it is not.
Worked example
Example: 5 g in 250 mL
Defaults: solute 5 g, volume 250 mL.
- Divide: 5 / 250 = 0.02.
- Percent: 0.02 x 100 = 2% w/v.
- Liters: 250 mL = 0.25 L, so 5 / 0.25 = 20 g/L.
- mg/mL: 5 / 250 x 1000 = 20 mg/mL.
- Tool shows 2% w/v, 20 g/L, 20 mg/mL.
Reference table
| Mix | Percent | g/L |
|---|---|---|
| 0.9 g in 100 mL saline | 0.9% w/v | 9 g/L |
| 2 g in 100 mL | 2% w/v | 20 g/L |
| 5 g in 100 mL | 5% w/v | 50 g/L |
| 10 g in 100 mL | 10% w/v | 100 g/L |
Limits
- w/v only; w/w and v/v need masses or volumes of both parts.
- Assumes volumes add neatly, which fails for strong syrups.
- No purity correction; technical grade solutes run under 100%.
- Prep guide only, never a dosing instruction.
Common mistakes
- Adding solute to 100 mL water instead of filling to 100 mL.
- Confusing w/v with w/w on thick mixes.
- Reading 0.9% saline as 0.9 g per liter.
- Scaling by eye instead of recalculating g/L.
- Trusting kitchen spoons for gram level work.
Try it yourself
Quick checks. Answers sit tucked under each question.
10 g in 100 mL?
10 / 100 x 100 = 10% w/v, 100 g/L, 100 mg/mL.
1 g in 500 mL?
1 / 500 x 100 = 0.2% w/v, 2 g/L, 2 mg/mL.
2.5 g in 50 mL?
2.5 / 50 x 100 = 5% w/v, 50 g/L.
Questions
What does 2% w/v mean?
2 g of solute per 100 mL of finished solution.
How is that different from w/w?
w/w divides by solution mass; w/v divides by solution volume.
What is saline in g/L?
0.9% means 9 g per liter.
Why fill to the mark after dissolving?
Solute volume shifts the total, so premeasured water overshoots.
Can I scale 2% to 2 liters?
Yes: 20 g/L times 2 is 40 g, filled to 2 L.
Is percent the same as molarity?
No. Molarity divides moles by liters; convert with molar mass.