Molarity from Percent Calculator

Turn a reagent bottle label into a usable molarity.

Written and maintained by Mohit PatelLast checked August 4, 2026How we build these

Concentration by mass

From the bottle label. Bench HCl is 37%, sulfuric 98%, nitric 70%.

Density

g/mL

Also on the label. HCl 1.19, H₂SO₄ 1.84, HNO₃ 1.42.

Or name the compound

Optional. Type a name like sucrose or a formula like CuSO4·5H2O and the molar mass is filled in for you. Leave blank to use the number below.

Molar mass

g/mol

Molarity of the stock solution

12.076 M

440.3 g/L at 37.0% and 1.19 g/mL

Molarity12.0762 mol/L

Grams per litre440.3 g/L

Molality16.1081 mol/kg

To make 1 L of 1 M, dilute82.81 mL up to 1 L

M = 10 × (% w/w) × density ÷ molar mass. The 10 converts grams per 100 g into grams per litre, and this is the calculation that turns a reagent label into something you can dilute from — bench hydrochloric acid at 37% and 1.19 g/mL comes out at 12.1 M. Density is essential and cannot be assumed to be 1. Concentrated sulfuric acid is 1.84 g/mL, so ignoring it would understate the molarity by nearly half. Always add concentrated acid to water rather than the reverse. The dilution is strongly exothermic and adding water to acid can boil it back out of the vessel.

How the Molarity from Percent Calculator works

Enter the mass percentage and density from the label, plus the molar mass, and this returns the molarity of the stock solution — along with how much to take for a litre of 1 M. This is the calculation that turns 37% and 1.19 g/mL into 12.1 M hydrochloric acid.

Also known as: percent to molarity converter · molarity of concentrated hcl · w/w to molarity calculator · molarity of concentrated acid

Where to go next

The Molarity from Percent question rarely arrives on its own. These are the ones that usually come with it:

Molarity Calculator — Moles per litre of solution — not of solvent.
Dilution Calculator — M₁V₁ = M₂V₂, with the diluent volume you actually need.
Mass Percent Solution Calculator — w/w, w/v and v/v — which are not interchangeable.
Speed Distance Time Calculator — Any one of the three from the other two, in four units.

Sources

Frequently asked questions

How do I convert percent by mass to molarity?

M = 10 × (% w/w) × density ÷ molar mass. The 10 converts grams per 100 g of solution into grams per litre.

What is the molarity of concentrated hydrochloric acid?

About 12.1 M, from 37% by mass at a density of 1.19 g/mL and a molar mass of 36.46 g/mol. Concentrated sulfuric acid is 18.4 M and concentrated nitric is about 15.8 M.

Why do I need the density?

Because percent by mass relates the solute to the solution's mass while molarity relates it to volume. Density is the only bridge between the two, and assuming 1 g/mL would understate concentrated sulfuric acid's molarity by nearly half.

How do I dilute from the stock safely?

Add the acid to the water, never the reverse. Diluting concentrated acid is strongly exothermic and adding water to acid can flash-boil it out of the vessel.

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