PPM to Molarity Calculator
Convert ppm ↔ molarity (mol/L, mM, µM, nM) with molecular weight and solution-density correction. Also converts mg/L, ppb, ppt and % — 100% free, runs entirely in your browser.
This tool converts between mass concentration and molarity — it needs a molecular weight. For a pure unit conversion ppm ↔ ppb ↔ ppt (no chemistry, no molecular weight), use our ppm to ppt converter. Dosing a reef aquarium? See reef dosing calculator.
Converter
Enter a concentration in any unit, the molecular weight (pick a preset or type your own), and the solution density. Results update live.
Quick ppm ↔ ppb ↔ ppt panel
Pure unit conversion — no molecular weight needed. Type in any box.
Worked examples
M = 100 ÷ (58.44 × 1000) = 0.0017112 mol/L = 1.7112 mM = 1711.2 µM.
ppm = 0.01 × 100.0869 × 1000 = 1000.869 ppm ≈ 1000.9 ppm.
What "ppm" actually means
ppm = parts per million by mass: 1 ppm = 1 mg of solute per 1 kg of solution (w/w). It is not "per liter" — that shortcut only works when the solution density is 1 kg/L (dilute water solutions).
- ppm (w/w) = mg solute ÷ kg solution. Always true, any liquid.
- mg/L (w/v) = mg solute ÷ L solution. Equals ppm only if ρ = 1 kg/L. Convert: mg/L = ppm × ρ.
- Density caveat: brines, syrups, acids and solvents have ρ ≠ 1. Always enter the real density above for non-aqueous or concentrated solutions.
- "ppt" is ambiguous: in chemistry it usually means parts per trillion (10⁻¹²), but in oceanography/salinity it means parts per thousand (10⁻³) — seawater at "35 ppt salinity" is 35,000 ppm, not 35 parts per trillion. Check your source.
Common ions & compounds — molecular weights
Tap a row to load it into the converter.
| Substance | Formula / ion | MW (g/mol) |
|---|
Frequently asked questions
What is the formula to convert ppm to molarity?
Molarity (mol/L) = ppm ÷ (molecular weight × 1000) for dilute water solutions where density ≈ 1 kg/L. With a different solution density ρ (kg/L), use M = ppm × ρ ÷ (MW × 1000). Example: 100 ppm NaCl (MW 58.44) gives 100 ÷ (58.44 × 1000) = 0.0017112 mol/L, i.e. 1.7112 mM.
How do I convert 2 ppm chlorine to molarity?
Chlorine gas Cl₂ has MW 70.90 g/mol. M = 2 ÷ (70.90 × 1000) = 0.000028209 mol/L = 0.028209 mM = 28.21 µM. (For 50 ppm the same math gives 0.70522 mM.)
How many ppm is 1 M NaCl?
ppm = M × MW × 1000 ÷ ρ. For 1 mol/L NaCl (MW 58.44, ρ = 1): 1 × 58.44 × 1000 = 58,440 ppm, which is 5.844% w/w.
Does solution density change the ppm to molarity conversion?
Yes — ppm is mass-based (mg/kg) while molarity is volume-based (mol/L), so density is the bridge. 1000 ppm calcium (MW 40.078) in a brine of density 1.25 kg/L gives 0.031189 mol/L, versus 0.024951 mol/L at density 1.000 — ignoring density causes a 25% error here.
Is 1 ppm always equal to 1 mg/L?
Only when the solution density is exactly 1 kg/L, as in dilute water solutions. In general mg/L = ppm × ρ. Example: 1000 ppm in a solution of density 0.98 kg/L is 980 mg/L, not 1000 mg/L.
How do I convert ppm to ppb and ppt?
These are pure unit conversions needing no molecular weight: ppb = ppm × 1000, and ppt (parts per trillion) = ppm × 1,000,000. So 2.5 ppm = 2,500 ppb = 2,500,000 ppt.
How many ppm are in 1 percent?
1% = 10,000 ppm. Conversely 1 ppm = 0.0001%. So 0.9% physiological saline is 9,000 ppm NaCl.
How do I convert 0.01 M CaCO₃ to ppm?
ppm = M × MW × 1000 ÷ ρ = 0.01 × 100.0869 × 1000 = 1000.869 ppm, about 1000.9 ppm at density 1 kg/L.
The EPA lead limit is 15 ppb — what is that in molarity?
15 ppb = 0.015 ppm. Lead (Pb) MW 207.2 g/mol: M = 0.015 ÷ (207.2 × 1000) = 0.000000072394 mol/L = 72.39 nM.
How do I convert water hardness (ppm as CaCO₃) to molarity?
Water hardness is reported as mg/L as CaCO₃ (MW 100.0869). 150 ppm as CaCO₃ → 150 ÷ (100.0869 × 1000) = 0.0014987 mol/L = 1.4987 mM.
Why can't I convert ppm to molarity without molecular weight?
ppm counts mass while molarity counts molecules (moles) — molecular weight is the bridge between the two, so it is required. Conversions like ppm ↔ ppb ↔ ppt need no molecular weight because they are all mass ratios; for those use a plain unit converter instead.
How do I convert 1 µM to ppm?
ppm = M × MW × 1000 ÷ ρ. 1 µM = 10⁻⁶ mol/L, so for NaCl (MW 58.44): 0.000001 × 58.44 × 1000 = 0.05844 ppm.
How many ppm is 0.025 M glucose?
Glucose MW 180.156 g/mol: ppm = 0.025 × 180.156 × 1000 = 4503.9 ppm at density 1 kg/L.
Nitrate reported "as N" vs "as NO₃⁻" — how do I convert?
Multiply by the mass ratio 62.004 ÷ 14.007 = 4.4266. So 10 ppm nitrate-N equals 44.266 ppm as NO₃⁻. Always check which basis your lab report uses before comparing to limits.
Related tools
Pure unit conversion without chemistry: ppm to ppt converter (ppm ↔ ppb ↔ ppt) · Aquarium dosing: reef dosing calculator
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