Grams to Moles Converter
Enter a mass, an amount in moles or a number of particles, plus the substance's formula or molar mass, and get the other two quantities back with the factor-label working written out. It rounds to the significant figures your data deserve. Free, no sign-up.
Case matters: Co is cobalt, CO is carbon monoxide. Hydrates use · or *, charges use ^ (Fe^3+).
Results
25.0 g
Mass
0.428 mol
Amount of substance
2.58 × 10²³
Particles
The working
Molar mass of NaCl: M = 58.44 g/mol
25 g × (1 mol / 58.44 g) = 0.4278 mol
0.4278 mol × (6.02214076 × 10²³ particles / 1 mol) = 2.58 × 10²³ particles
Intermediate results carry one extra digit; only the final answers are rounded to 3 significant figures.
Atoms of each element in the sample
| Element | Atoms per formula unit | Atoms in the sample |
|---|---|---|
| Sodium (Na) | 1 | 2.58 × 10²³ |
| Chlorine (Cl) | 1 | 2.58 × 10²³ |
How to Use the Grams to Moles Converter
- 1. Name the substance. Type its formula, such as NaCl or Ca(OH)2, and the converter works out the molar mass from IUPAC atomic weights. If you have no formula, choose "A molar mass" and type the figure in g/mol.
- 2. Say what you know. Pick mass, amount (moles) or number of particles, then enter the value. Mass can be in µg, mg, g or kg, and the amount in µmol up to kmol; large counts can be written 6.02e23.
- 3. Choose the rounding. The default matches the answer to the significant figures of your data. You can fix it at three to six figures instead.
- 4. Read the three quantities and the working. Mass, moles and particles are all shown, with the factor-label lines and, for a formula, the atoms of each element in the sample.
The Mole Conversions
The mole links the mass you weigh to the number of particles you cannot see. Two conversion factors do all the work: the molar mass M (grams per mole, specific to the substance) and the Avogadro constant NA, which is exactly 6.02214076 × 10²³ per mole by the definition of the SI since 2019.
Grams to moles
n = m / M
Moles to grams
m = n × M
Moles to particles
N = n × N_A
Particles to moles
n = N / N_A
In the factor-label method each conversion is a fraction equal to one, arranged so the unwanted unit cancels: 25.0 g × (1 mol / 58.44 g) leaves moles. That is the form the converter prints.
Worked Examples
Grams to moles to particles. How many moles and formula units are in 25.0 g of sodium chloride? The molar mass of NaCl is 22.99 + 35.45 = 58.44 g/mol (these are the converter's default inputs).
- Moles: 25.0 g × (1 mol / 58.44 g) = 0.4278 mol, which is 0.428 mol to three significant figures.
- Formula units: 0.4278 mol × 6.022 × 10²³ per mol = 2.58 × 10²³ formula units.
- Atoms: each formula unit has one Na and one Cl, so there are 2.58 × 10²³ atoms of each element.
Moles to grams. What mass is 0.250 mol of NaCl? 0.250 mol × (58.44 g / 1 mol) = 14.61 g, or 14.6 g to three significant figures.
Particles to grams. What do 1.50 × 10²⁴ water molecules weigh? (1.50 × 10²⁴) ÷ (6.022 × 10²³ per mol) = 2.491 mol, and 2.491 mol × 18.015 g/mol = 44.87 g, so 44.9 g.
Which particle are you counting?
One mole of H2O is 6.022 × 10²³ molecules, but it holds twice that many hydrogen atoms and as many oxygen atoms. For ionic compounds such as NaCl the countable unit is the formula unit, not a molecule. The table under the working multiplies the particle count by each element's subscript so you can read off atoms directly. For solutions, the next step is the Molarity Calculator.
Common Mistakes
- Using the atomic mass of an element that exists as molecules. Oxygen gas is O2 with M = 31.998 g/mol, not 15.999. Type the formula as it exists: O2, N2, Cl2, P4, S8.
- Forgetting the unit prefix. 250 mg is 0.250 g. Pick the unit instead of converting by hand.
- Dividing when you should multiply. Going from grams to moles divides by M; going from moles to grams multiplies. The units tell you: g ÷ (g/mol) leaves mol.
- Over-stating precision. A 2-figure mass gives a 2-figure answer even though the calculator holds more digits. The Significant Figures Calculator explains the rules.
- Mixing formula units and molecules. Count NaCl as formula units; count H2O as molecules.
Frequently Asked Questions
- How do you convert grams to moles?
- Divide the mass in grams by the molar mass in g/mol. For 25.0 g of NaCl (58.44 g/mol), 25.0 ÷ 58.44 = 0.428 mol. Find the molar mass first by adding the atomic weights of every atom in the formula.
- How do you convert moles to grams?
- Multiply the number of moles by the molar mass. 0.250 mol of NaCl is 0.250 × 58.44 = 14.6 g. The mole units cancel and grams are left.
- How many molecules are in a given number of grams?
- Convert grams to moles, then multiply by the Avogadro constant, 6.022 × 10²³ per mole. For 10.0 g of water, 10.0 ÷ 18.015 = 0.555 mol, which is 3.34 × 10²³ molecules. This converter does both steps and shows them.
- Is the Avogadro constant exact?
- Yes. Since the SI redefinition that took effect in May 2019, the Avogadro constant is defined as exactly 6.02214076 × 10²³ per mole, so it never limits the significant figures of an answer. The molar masses come from measured atomic weights, which do have uncertainties.
- Does a mole of every substance weigh the same?
- No. A mole always contains the same number of particles, but each substance's particles have different masses, so a mole of carbon is 12.011 g and a mole of lead is 207.2 g. That is why every conversion needs the molar mass.
- How many significant figures should a mole calculation have?
- Match the least precise measurement. If you weighed 25.0 g (three figures), report moles to three figures even if the molar mass has five. The converter's default setting follows that rule; you can override it for a fixed number of figures.