Refractometer & Brix Calculator
Calculate refractive index, concentration from refractometry, and Brix for sugar solutions.
What Refractive Index Reveals
Refractive index measures how much light slows in a medium, which depends on electron density — and therefore on how much dissolved material is present. Because it is fast, needs one drop, and requires no reagents, refractometry is the standard field method for sugar content.
Brix is defined as the sucrose concentration in g per 100 g of solution that would give the same refractive index. A reading of 20 °Bx means the sample refracts like a 20% sucrose solution — not that it contains exactly 20% sucrose.
| Application | Typical range | Note |
|---|---|---|
| Grape must at harvest | 18–26 °Bx | Predicts potential alcohol |
| Fruit juice | 10–16 °Bx | Ripeness indicator |
| Honey | ~80 °Bx | Very concentrated |
| Maple syrup | 66 °Bx | Legal minimum in many regions |
Two Corrections That Matter
Temperature. Refractive index falls as temperature rises, roughly 0.0001 per degree for aqueous solutions. Field refractometers include automatic temperature compensation; without it, a reading taken in a warm vineyard can be a full degree Brix off.
Other dissolved solids. Anything dissolved contributes, so acids, salts and glycerol all inflate the apparent Brix. In grape must the error is small, but in fermenting wine the alcohol produced has a lower refractive index than the sugar it replaced, so Brix readings become unreliable once fermentation starts — hydrometry is used instead.
In polymer science the same instrument serves a different purpose. The refractive index increment dn/dc is essential for light scattering molecular weight determination, where scattered intensity depends on (dn/dc)² — so a small error in dn/dc doubles in the final molecular weight.
Worked Examples
Common Mistakes
Refractive index shifts about 0.0001 per degree. An uncompensated reading in warm conditions can be a full degree Brix in error.
Alcohol has a lower refractive index than the sugar it replaced, so Brix readings become unreliable once fermentation begins. Use a hydrometer instead.
Brix is the sucrose-equivalent reading. Acids, salts and other solutes contribute, so actual sugar content is somewhat lower.
The refractive index increment depends on the polymer–solvent pair. Because scattered intensity scales with (dn/dc)², errors are amplified in the molecular weight.
Frequently Asked Questions
Formula Explorer connections
Interpretation: This analytical relationship converts an instrument signal, separation measure or optical response into concentration, identity or performance. Assumption: Calibration, blank correction, linear range, path length, matrix effects and instrument settings must match the sample and method.