Percentage strength for urea is read as % w/v: grams of solute in 100 mL of solution. So 1% is 1 g per 100 mL, which for this compound works out at 0.16651 mol/L, and 0.9% is 9 g per litre or 0.14986 mol/L. The calculator takes a percentage and a volume and returns the grams to weigh, with the molarity and mg/mL equivalents beside it.
The figure comes from the formula. Urea is 12.011 (C) + 4 × 1.008 (H) + 2 × 14.007 (N) + 15.999 (O), which is 60.056 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Nitrogen makes up the largest share of the mass: 2 of the 8 atoms in a formula unit are nitrogen, and they account for 28.014 g of the 60.056 g, or 46.65% by mass. The derivation table below breaks the whole molecule down element by element.
Three different percentages are in circulation and they are not interchangeable. Per cent w/v is mass in a volume, the one used here and on medical labels; per cent w/w is mass in mass, the one on drums of concentrated reagent; per cent v/v is volume in volume, used for liquids mixed into liquids. For a dilute aqueous solution w/v and w/w are within a percent of each other, but for anything concentrated the density has to come into it.
The nitrogen fertiliser with the highest nitrogen content, a skin humectant, and the compound the body uses to excrete nitrogen — reported as BUN. At 60.056 g/mol it is heavier than 3 of the 21 organic compounds covered here, and that ranking matters more than it looks: acetone has a molar mass of 58.08 g/mol, so a gram of it contains 3.4% more formula units than a gram of urea. Weigh by mass and you are not weighing equal amounts of substance.
Two practical things move the result. Purity below 100% means the weighed mass overstates how much compound you have — at 98% assay, 1.2011 g of every 60.056 g is not the compound — and any water picked up from the air does the same. Both are systematic, so they shift every solution made from that jar in the same direction.
The formula
p- The strength you want, as % w/v
V- The volume of solution, in millilitres
m- The mass of urea to weigh out, in grams
60.056- The molar mass of urea in g/mol, derived from its formula
How it works, step by step
- Enter the percentage strength you want, as % w/v.
- Enter the volume of solution in millilitres.
- Grams needed is percentage × volume ÷ 100, since 1% w/v is 1 g per 100 mL.
- The molarity that strength corresponds to for urea is shown beneath, using 60.056 g/mol.
Worked examples
0.9% w/v urea in 500 mL
0.9% w/v is 0.9 g per 100 mL, so 500 mL needs 4.5 g. In molar terms that solution is 0.14986 mol/L, and it is 9 mg/mL if you are dosing by volume.
5% w/v urea in 100 mL
5% w/v is 5 g per 100 mL, so 100 mL needs 5 g. In molar terms that solution is 0.83256 mol/L, and it is 50 mg/mL if you are dosing by volume.
10% w/v urea in 1000 mL
10% w/v is 10 g per 100 mL, so 1000 mL needs 100 g. In molar terms that solution is 1.6651 mol/L, and it is 100 mg/mL if you are dosing by volume.
How to read your score
Frequently asked questions
What is the molar mass of urea (CH4N2O)?
It is 60.056 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 12.011 (C) + 4 × 1.008 (H) + 2 × 14.007 (N) + 15.999 (O). One mole of urea therefore weighs 60.056 g, and a gram of it is 16.651 mmol.
What percentage of urea is nitrogen?
46.65% by mass. Each formula unit contains 2 nitrogen atoms contributing 28.014 g of the 60.056 g total, so 100 g of urea contains 46.65 g of nitrogen and a kilogram contains 466.46 g of it.
How many grams of urea make a 1% w/v solution?
1 g in 100 mL of solution, 5 g in 500 mL, 10 g in a litre. The percentage is fixed to the volume, not to the compound, so those masses are the same whatever is being dissolved — what changes with the compound is the molarity they come to.
What molarity is a 1% w/v solution of urea?
0.166511 mol/L, because 1% w/v is 10 g/L and 60.056 g/L is one molar. A 0.9% solution is 0.14986 mol/L and a 5% solution is 0.83256 mol/L.
Is % w/v the same as % w/w?
No. Per cent w/v is grams per 100 mL of solution; per cent w/w is grams per 100 g of solution. They coincide only when the solution has a density of 1.00 g/mL, which dilute aqueous solutions approximately do and concentrated ones do not. Labels on concentrated reagents are usually w/w.
What is 1% w/v in mg/mL?
10 mg/mL, since 1 g in 100 mL is 1000 mg in 100 mL. For urea that is also 166.51 mmol/L, which is the form a dose calculation usually wants.
Percentage strengths of urea
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Nitrogen (N) | 2 | 14.007 | 28.014 | 46.65% |
| Oxygen (O) | 1 | 15.999 | 15.999 | 26.64% |
| Carbon (C) | 1 | 12.011 | 12.011 | 20% |
| Hydrogen (H) | 4 | 1.008 | 4.032 | 6.714% |
| Total — one mole of urea | 60.056 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 60.056 g/mol.
| Strength | per 100 mL | per 500 mL | per 1 L | Molarity (mol/L) |
|---|---|---|---|---|
| 0.1% w/v | 100 mg | 500 mg | 1 g | 0.016651 |
| 0.25% w/v | 250 mg | 1.25 g | 2.5 g | 0.041628 |
| 0.5% w/v | 500 mg | 2.5 g | 5 g | 0.083256 |
| 0.9% w/v | 900 mg | 4.5 g | 9 g | 0.14986 |
| 1% w/v | 1 g | 5 g | 10 g | 0.16651 |
| 2% w/v | 2 g | 10 g | 20 g | 0.33302 |
| 3% w/v | 3 g | 15 g | 30 g | 0.49953 |
| 5% w/v | 5 g | 25 g | 50 g | 0.83256 |
| 10% w/v | 10 g | 50 g | 100 g | 1.6651 |
| 20% w/v | 20 g | 100 g | 200 g | 3.3302 |
A 1% w/v solution is 1 g in 100 mL, which for this compound is 0.16651 mol/L because 10 g/L divided by 60.056 g/mol gives that figure.
| Compound | Formula | Molar mass (g/mol) | Millimoles in 1 g |
|---|---|---|---|
| Methanol | CH4O | 32.042 | 31.209 |
| Ethanol | C2H6O | 46.069 | 21.707 |
| Acetone | C3H6O | 58.08 | 17.218 |
| Urea (this page) | CH4N2O | 60.056 | 16.651 |
| Isopropyl alcohol | C3H8O | 60.096 | 16.64 |
| Ethylene glycol | C2H6O2 | 62.068 | 16.111 |
| Glycine | C2H5NO2 | 75.067 | 13.321 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.