PPM calculator

What ppm means

In solution chemistry, ppm (parts per million) is a ratio by mass: ppm = mass of solute ÷ mass of solution × 10⁶. One ppm is 1 mg of solute in each kilogram of solution. ppb (parts per billion) is the same ratio × 10⁹, or µg/kg, and 1 % by mass (% w/w) is 10,000 ppm.

Because ppm compares two masses, it says nothing about volume. Converting it to mg/L needs the solution's density, which is why the calculator asks for one whenever a conversion crosses from mass to volume. NIST's SI guide notes that ppm, ppb and ppt are not SI units and recommends naming the basis instead, as in mg/kg. The billion is ambiguous too: in some countries a billion is 10¹², not 10⁹. This calculator always means ppm and ppb by mass. It does not convert ppm by volume, as used for gases.

ppm to mg/L

Mass per volume is the mass fraction times the density: mg/L = ppm × density (g/mL). Choose Convert a concentration, enter the value in ppm, choose mg/L under Convert to, and enter the solution density. The table under the result shows the same concentration in every other unit.

A dilute water solution near room temperature has a density close to 1 g/mL, so its ppm and mg/L values are nearly equal. Water is roughly 1 g/mL, but its density changes with temperature and with dissolved substances. Press Dilute water · 1.00 g/mL to fill in that value, or enter your solution's own density. In a denser solution the two differ: 250 ppm at 1.2 g/mL is 300 mg/L.

ppm to mg/mL and µg/mL

One mg/mL is 1,000 mg/L, so at a density of 1 g/mL, 1 mg/mL is 1,000 ppm. One µg/mL equals 1 mg/L, so at 1 g/mL a µg/mL value and a ppm value are the same number. Saline at 0.9 % w/v, which is 0.9 g per 100 mL, is 9 mg/mL or 9,000 mg/L.

ppm, ppb and percent

These three are all mass fractions, so converting between them needs no density:

For example, OpenStax works through lead in tap water at 15 ppb: that is 0.015 ppm.

How much solute for a ppm solution

Choose Solute for a target. The mass of solute is the target mass fraction times the mass of the final solution: solute = ppm × 10⁻⁶ × solution mass. For 50 ppm in 2 L of a dilute water solution (1.00 g/mL, so 2,000 g), weigh 100 mg and make the final solution up to 2 L.

If you weigh the whole solution instead, choose kg or g for the amount and no density is needed. The total includes the solute itself: a 50.0 g sample at 9.6 ppm holds 0.48 mg, as in OpenStax's mercury exercise. Targets in mg/L or other mass-per-volume units multiply by the volume directly. In the lead example, 15 ppb in a 300 mL glass at about 1.00 g/mL is 4.5 µg.

Dilute a stock to a ppm target

Choose Stock for a target. With both concentrations in mass per volume, V₁ = C₂ × V₂ ÷ C₁. To bring 500 mL to 50 ppm (50 mg/L at 1.00 g/mL) from a 1,000 mg/L stock, take 25 mL of stock and make it up to 500 mL: a 20-fold dilution.

A stock or a target in ppm, ppb or % w/w needs its own density, because a concentrated stock can be denser than the final solution. For molar stocks and other units, the dilution calculator covers C₁V₁ = C₂V₂ as well.

NMR: convert ppm to Hz

In NMR spectroscopy, ppm measures a chemical shift: δ = (ν − ν_ref) ÷ ν_ref, where "ppm" stands for × 10⁻⁶. Because a frequency difference is in Hz and the spectrometer frequency in MHz, Hz = ppm × MHz. Choose NMR shift · ppm and Hz:

• 0.1 ppm of ¹H on a 400 MHz spectrometer is 40 Hz.
• A 7 Hz splitting there spans 0.0175 ppm.

Other nuclei resonate at their own frequency in the same magnet. IUPAC lists each as a ratio Ξ to the ¹H frequency of tetramethylsilane (TMS): 25.14502 % for ¹³C, for example. On a 400 MHz instrument ¹³C therefore resonates at 100.58 MHz, and 1 ppm of ¹³C there is 100.58 Hz. Choose the observed nucleus and the calculator applies its ratio. For the best precision, use the exact frequency from your acquisition parameters; the nominal 400 is rounded.

ppm to molarity

Molarity is the mass per volume divided by the molar mass. 250 ppm at 1.2 g/mL is 0.3 g/L, which at 100 g/mol is 3 mM. Enter a molar mass above to add M, mM and µM to the table. The molarity calculator also finds the mass or volume for a target molarity and reads molar masses from chemical formulas.

Limits

• ppm and ppb are by mass. Volume ratios for gases (ppmv) and the ambiguous "ppt" are not converted.
• The density belongs to the whole solution at its temperature. The calculator does not correct for temperature, and a missing density is refused rather than assumed.
• Dilution volumes assume volumes add; make up to the final volume when precision matters.
• NMR conversions use the nominal ¹H frequency you enter and IUPAC's Ξ ratios. They do not correct for referencing, solvent or temperature effects on the shift itself.

Calculations run in your browser. Copy calculation and Save calculation export your inputs and result as text; nothing is uploaded.

Sources: OpenStax, Chemistry 2e, 3.4 Other Units for Solution Concentrations (ppm and ppb by mass; Example 3.25, lead at 15 ppb, assuming tap water at about 1.00 g/mL; the mercury exercise, 0.48 mg in 50.0 g = 9.6 ppm; mass-volume percent). NIST, Guide for the Use of the International System of Units, SP 811, section 7.10.3 (ppm, ppb and ppt). USGS Water Science School, Water Density. Harris R. K. et al., Further Conventions for NMR Shielding and Chemical Shifts (IUPAC Recommendations 2008), Pure and Applied Chemistry 80, 59–84 (equation 1; Appendix 1, Ξ values). All read October 6, 2026.