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Refractive Index → Concentration

Read a refractometer value (n_D at 20 °C) and convert it to solution concentration, or go the other way, for several common substances, using tabulated reference curves.

How to use this tool

Turn a refractometer reading into a concentration. Pick what you're measuring, type the refractive index, and the tool looks up the matching concentration from a reference curve, or run it backwards to predict the reading for a known concentration.

What to enter

Substance: the solution you're measuring (sucrose/°Brix, ethanol, glycerol, NaCl, sulfuric acid). This selects the reference curve.
Refractive index n_D: the value off your refractometer, read at 20 °C (e.g. 1.3479). Bench refractometers usually temperature-correct automatically.
Concentration: leave blank to solve for it, or type a value to get the expected refractive index instead. Edit either field; the other updates.

Reading the result

You get the concentration in the substance's natural unit (°Brix for sucrose, % w/w for the rest) and the matching n_D, plus the tabulated range the curve covers. Readings outside that range return no result rather than an unreliable extrapolation.

Worked example

A sucrose solution reading n_D = 1.3479 interpolates to roughly 10 °Brix, i.e. about 10 % sucrose by mass.

Measurement

Substance

Refractive index n_D at 20 °C

Concentration % w/w

Edit either field, the other is interpolated from the reference curve.

Result

Concentration and n_D update together, fill in whichever you measured. The tabulated range shows the limits of the reference curve; a value outside it returns no result rather than an unreliable extrapolation. Read at 20 °C, or use a temperature-correcting refractometer.

Methodology

Each substance has a tabulated, monotonic curve of refractive index versus concentration at 20 °C. The tool interpolates linearly between the nearest two tabulated points in either direction. Sucrose uses the ICUMSA °Brix scale (% sucrose by mass).

Sources

Refractive-index tables from the CRC Handbook (97th ed.); sucrose from the ICUMSA Brix tables.

Known limits

Results are temperature-sensitive: a value measured away from 20 °C must be temperature-corrected first (most bench refractometers do this automatically).
Valid only inside each substance's tabulated range; out-of-range inputs return no result rather than an extrapolation.