Percentage Concentration to Molarity Calculator
Convert percentage concentration to molarity from density and molar mass.
Supports 11 density units, 11 molarity volume units, 3 molar mass units, and 13 preset substances.
Updated September 5, 2026
What this calculator does
Bottles in the lab are labeled in percent — “37% hydrochloric acid”, “96% sulfuric acid” — but protocols call for molarity, like 1 M or 6 M. This calculator bridges that gap: give it percentage, solution density, and molar mass, and it returns molarity. It also works backwards, so you can recover any one of the four values from the other three.
The one thing most people miss: percent alone is not enough. You need the solution density, because a liter of concentrated acid weighs much more than a liter of water.
It is built for students preparing dilutions, technicians checking a stock bottle, and anyone who needs to turn a supplier label into a number they can pipette from. Pick one of the 13 built-in substances — hydrochloric acid, sulfuric acid, sodium hydroxide, ethanol, glucose, and more — or type a custom molar mass for anything else.
How to use it
Fill in the three values you know and leave the unknown blank — the missing field is computed automatically and shown in blue. Editing any computed field re-solves the rest, so you can work in whichever direction your problem demands.
Choose your substance
Select a preset such as Hydrochloric acid to lock in its molar mass, or choose the custom option and type the molar mass yourself.
Enter percentage and density together
Type the label percentage (0–100, mass basis) and the density of that same solution — for example 1.19 g/cm³ for concentrated HCl. Match the units to your source; g/cm³ and g/mL are the most common on data sheets.
Read the molarity and use it
The computed molarity is the stock concentration on your bottle. Use it directly in a dilution plan or to check whether a label claim is plausible.
Worked example — concentrated hydrochloric acid
A reagent bottle says 37% HCl, density 1.19 g/cm³. Select the Hydrochloric acid preset (molar mass 36.46 g/mol), enter 37 for percentage and 1.19 for density. The calculator returns about 12.08 M:
Note the density conversion tucked inside: 1.19 g/cm³ equals 1190 g/L, which is the unit the formula actually uses. That single step is where most hand calculations go wrong.
The formula, explained
Percentage here means mass percent (w/w): grams of solute per 100 grams of solution. Multiplying by the solution density converts that into grams per liter, and dividing by molar mass converts grams into moles. The full relationship is:
Core relationship
Molarity from percentage, density, and molar mass
Molarity
Moles of solute per liter of solution, in mol/L (same as mol/dm³). This is usually the value you solve for.
Percentage
Mass percent (w/w), between 0 and 100. Grams of solute per 100 grams of solution — not per 100 mL.
Density
Solution density in g/L. The field defaults to g/cm³, so 1.19 g/cm³ becomes 1190 g/L internally.
Molar mass
In g/mol — typed by you or locked in by a preset. Preset values match standard references, e.g. HCl at 36.46 g/mol and sulfuric acid at 98.08 g/mol (see the PubChem hydrochloric acid record and the PubChem sulfuric acid record).
One equation, four directions — solve for any unknown
Solve for percentage
Solve for density
The same rearrangement logic recovers molar mass too — just leave that field blank in custom mode. Two practical consequences follow. First, density is not optional decoration: for concentrated solutions it differs sharply from water, so substituting 1.0 g/mL silently corrupts the answer. Second, the percentage must be mass-based; a volume percent (v/v) label, common for ethanol–water mixtures, needs a different calculation and should not be fed into this formula.
Real-world examples
Checking a concentrated sulfuric acid bottle
A stock bottle reads 96% H₂SO₄, density 1.84 g/cm³. With the Sulfuric acid preset (98.08 g/mol), the molarity is:
About 18 M is the well-known strength of concentrated sulfuric acid. If your result lands far from that for a “concentrated” label, re-check the density — a stale or mistyped density is the usual culprit. Once you trust the stock strength, plan the actual dilution with a dilution factor calculator.
Working backwards from a target molarity
Suppose an assay calls for roughly 6 M NaOH and you wonder what label percentage that corresponds to. Enter molarity 6, density 1.22 g/cm³ (the density of ~20% NaOH at room temperature), and molar mass 40 g/mol, leaving percentage blank:
So a ~20% w/w NaOH solution is about 6 M. This reverse direction is also how you sanity-check a supplier certificate: if the stated percentage, density, and molarity do not satisfy the equation, ask for a fresh assay. For solutions described by solute mass rather than percent, the mass percent calculator is the better starting point.
Tips and common mistakes
Always use the density of the actual solution. Density changes with concentration and temperature. Look it up for the stated percentage (supplier certificate or data sheet), not for pure water.
Confirm the percent basis. This calculator assumes w/w. If your label says v/v or w/v — common for disinfectants and ethanol blends — convert the basis first instead of forcing the number in.
Watch the g/cm³ vs. g/L factor of 1000. Entering 1190 when the unit says g/cm³ (instead of 1.19) inflates the answer a thousandfold. If a result looks absurd, this is the first place to look.
Remember presets hide the molar mass field. That is intentional: the value is fixed for the chosen substance. Switch back to the custom option if you need to type or solve for molar mass.
Frequently asked questions
Can I convert percent to molarity without density?
Not reliably. Percent tells you the mass ratio, but molarity needs moles per liter of solution — and only density connects mass of solution to volume. For dilute aqueous solutions near 1.00 g/mL the error is small, but for 37% HCl or 96% H₂SO₄ it is enormous, so always supply the real density.
Why does the calculator reject percentages above 100?
Mass percent cannot exceed 100% by definition — that would mean more solute than total solution. Values above 100 almost always come from mixing up w/v units (e.g. grams per 100 mL) with w/w percent, or from a typo.
When should I use the general molarity calculator instead?
When your starting point is a weighed mass and a volume rather than a percent label. Head to the molarity calculator if you dissolved, say, 5 g of NaCl in 500 mL — this page is specifically for the percent-plus-density route.
Limitations
- Results assume an ideal mass-percent (w/w) solution at the density you entered. Real densities shift with temperature and concentration, so treat answers as accurate to your input data — verify against the supplier certificate for critical work.
- The calculator does not account for volume contraction on mixing (notably ethanol–water), dissociation equilibria, or activity effects. For analytical standards, confirm by titration or an independent assay.
- Concentrated acids and bases in the presets are corrosive. Follow the reagent safety data sheet, wear appropriate protection, and add acid to water — never the reverse. This page computes concentrations; it is not a safety or procedural guide.
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