What is the molarity formula?

Molarity is c = n / V, where n is the amount of solute in moles and V is the volume of solution in litres. The unit is mol/L, also written M. Example: dissolve 0.5 mol of solute and make the solution up to 2 L and the molarity is 0.5 / 2 = 0.25 mol/L. Rearrange to find what you are missing: n = c times V, or V = n / c.

How do I find molarity from a mass in grams?

First convert mass to moles by dividing by the molar mass, then divide by the volume in litres. Combined: c = mass / (molar mass times volume). Example: 58.44 g of table salt NaCl, whose molar mass is 58.44 g/mol, dissolved to 1 L gives 58.44 / (58.44 times 1) = 1 mol/L, a 1 M solution. The from-mass mode does both steps and also tells you the grams to weigh for any target molarity.

Is mol/L the same as M?

Yes. M stands for molar and 1 M means 1 mole of solute per litre of solution, identical to 1 mol/L. So 0.1 M, 0.1 mol/L and 100 mmol/L all describe the same concentration. The capital M is the spoken and label shorthand; mol/L is the spelled-out SI-style form. This tool lets you read the answer in mol/L or mmol/L.

What is the difference between molarity and molality?

Molarity is moles per litre of solution; molality is moles per kilogram of solvent. The split matters because volume changes with temperature while mass does not, so a 1 M solution warmed up is no longer exactly 1 M, whereas a 1 molal solution stays 1 molal. Lab recipes and titrations almost always mean molarity, written M. This tool computes molarity, the everyday lab quantity.

How do I prepare a solution of a given molarity?

Decide the target molarity and final volume, then weigh out mass = molarity times molar mass times volume in litres. Example: for 0.25 L of 0.1 M sodium chloride, weigh 0.1 times 58.44 times 0.25 = 1.461 g, dissolve it, and top up to exactly 250 mL in a volumetric flask. The from-mass mode prints this weigh-out figure for you so you can read the recipe directly.

Why does the volume have to be in litres?

Because molarity is defined per litre. If you measured a volume in millilitres, divide by 1000 first: 250 mL is 0.25 L. This tool has a volume unit switch so you can type 250 and pick mL, and it converts internally before applying c = n / V. The most common molarity mistake is leaving the volume in mL, which makes the concentration come out 1000 times too large.

Prepare a buffer or reagent at the bench

You need 500 mL of 0.1 M sodium chloride for a protocol. Switch to the from-mass mode, type the molar mass 58.44, set the target through the weigh-out figure, and read that you need about 2.92 g. Weigh it, dissolve, and top up to 500 mL in a volumetric flask. The reverse recipe means you never have to do the milligram arithmetic in your head while standing at the balance.

Check a homework or exam answer

A chemistry problem gives 0.5 mol of a compound dissolved to 2 L and asks for the molarity. Type the moles and volume, solve for concentration, and the tool returns 0.25 mol/L so you can confirm your working. Flip the solve-for switch to practise the rearranged forms n = c times V and V = n / c with instant feedback.

Convert a clinical concentration into mmol/L

A result is quoted in mol/L but the report wants mmol/L, or vice versa. Enter the value, pick the concentration unit, and the answer is shown in the unit you chose. Because 1 mol/L is 1000 mmol/L, this removes the factor-of-a-thousand slip that creeps into lab and nursing maths under time pressure.

Teach the c = n / V relationship in class

Project the calculator, type 0.25 for concentration and 2 for volume, solve for moles, and the class watches n come out as 0.5 mol live. Change one number and the result updates instantly, which makes the proportional relationship between the three quantities obvious without a chalkboard full of rearranged formulas. Share the URL and every student opens the same worked example.

Molarity Calculator — Molar Concentration c = n / V

Molar concentration c = n / V — solve any one of moles, volume, concentration, or go straight from grams + molar mass — browser-only

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Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.

Solve for

Volume unitConcentration unit

Amount n (mol)Volume V (L)

Concentration c

0.25 mol/L

Molarity (mol per litre of solution) is not molality (mol per kilogram of solvent). Molarity shifts with temperature because volume expands; molality does not. Lab recipes almost always mean molarity, written M.

Every calculation runs in your browser. Nothing is uploaded.

What this tool does

Free molarity calculator for the work bench, the lecture hall and the homework set. Molarity is moles of solute per litre of solution, written mol/L or M, and the defining relation is c = n / V. Give the tool any two of amount of substance (mol), volume (L or mL) and concentration (mol/L or mmol/L) and it returns the third, so the same calculator covers "what molarity do I get", "how many moles are in this much", and "what volume holds this amount". A second mode starts from something you can actually weigh: enter the solute mass in grams or milligrams plus its molar mass, and it computes moles, then molarity with c = mass divided by molar mass times volume, and shows the reverse recipe so you know exactly how many grams to weigh out for a target concentration. Every result copies with one click and the share link reopens your exact numbers. 100 percent client-side, nothing is uploaded.

Tool details

Input: Numbers; The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output: Live result + Copy; The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy: Browser-side processing; The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share: Shareable URL state; Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget: Initial JS <= 9 KB; No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit: Calculator · Student; Category and role tags drive related tools, internal links, and quick fit checks.

How to use

1. Input

Paste or drop your content into the tool panel.
2. Process

Click the button. All processing is local in your browser.
3. Copy / Download

Copy the result or download to disk in one click.

How Molarity Calculator fits into your work

Use it for fast estimates, comparisons, and planning numbers before you make the final call.

Calculation jobs

Getting a realistic range before a purchase, plan, workout, or schedule decision.
Comparing scenarios by changing one input at a time.
Turning rough assumptions into a number you can discuss.

Calculation checks

Double-check units, dates, rates, and rounding assumptions.
Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
Save the inputs that produced an important result so you can reproduce it later.

Good next steps

These links move the current task into a more complete workflow.

Real-world use cases

Prepare a buffer or reagent at the bench
You need 500 mL of 0.1 M sodium chloride for a protocol. Switch to the from-mass mode, type the molar mass 58.44, set the target through the weigh-out figure, and read that you need about 2.92 g. Weigh it, dissolve, and top up to 500 mL in a volumetric flask. The reverse recipe means you never have to do the milligram arithmetic in your head while standing at the balance.
Check a homework or exam answer
A chemistry problem gives 0.5 mol of a compound dissolved to 2 L and asks for the molarity. Type the moles and volume, solve for concentration, and the tool returns 0.25 mol/L so you can confirm your working. Flip the solve-for switch to practise the rearranged forms n = c times V and V = n / c with instant feedback.
Convert a clinical concentration into mmol/L
A result is quoted in mol/L but the report wants mmol/L, or vice versa. Enter the value, pick the concentration unit, and the answer is shown in the unit you chose. Because 1 mol/L is 1000 mmol/L, this removes the factor-of-a-thousand slip that creeps into lab and nursing maths under time pressure.
Teach the c = n / V relationship in class
Project the calculator, type 0.25 for concentration and 2 for volume, solve for moles, and the class watches n come out as 0.5 mol live. Change one number and the result updates instantly, which makes the proportional relationship between the three quantities obvious without a chalkboard full of rearranged formulas. Share the URL and every student opens the same worked example.

Common pitfalls

Leaving the volume in millilitres. Molarity is per litre, so 250 mL must be entered as 0.25 L (or typed as 250 with the mL unit selected). Forgetting this makes the molarity come out 1000 times too large.
Confusing molarity with molality. Molarity is moles per litre of solution; molality is moles per kilogram of solvent. They are close in dilute aqueous solutions but diverge as concentration rises, and only molarity changes with temperature. Lab recipes almost always mean molarity.
Using mass instead of moles in c = n / V. The n in the formula is amount of substance in moles, not grams. Convert mass to moles first by dividing by the molar mass, or use the from-mass mode which does it for you.

Privacy

Every step here is plain JavaScript running in your browser tab: the c = n / V solve, the mass-to-moles conversion, the unit switches and the weigh-out recipe. No mass, volume or concentration you type is uploaded or logged. The one thing to know is that the shareable URL encodes your numbers in the query string, so a link pasted into chat records those values in the recipient server access log. For anything sensitive, use the copy button and paste the text instead of sharing the URL.

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Molarity Calculator — Molar Concentration c = n / V

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How Molarity Calculator fits into your work

Calculation jobs

Calculation checks

Good next steps

Real-world use cases

Prepare a buffer or reagent at the bench

Check a homework or exam answer

Convert a clinical concentration into mmol/L

Teach the c = n / V relationship in class

Common pitfalls

Privacy

FAQ

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