Compute the ideal path length from the Beer-Lambert law — enter absorbance, extinction coefficient and concentration.
Enter your target absorbance, molar extinction coefficient and concentration to find the right path length. Standard cells: 0.1 – 100 mm.
The Beer-Lambert law — A = ε · c · l — links absorbance (A), molar extinction coefficient (ε), concentration (c) and path length (l). Measurements are most reliable between A = 0.2 and 1.5; below that noise dominates, above that stray light and non-linearity creep in. Rearrange to l = A / (ε·c) and you get the path length that puts your sample in the sweet spot.
| Path length | Use case | scuvette option |
|---|---|---|
| 0.1 – 1 mm | Highly concentrated samples, high ε chromophores | ultra-micro cells |
| 2 – 5 mm | Concentrated samples, sub-micro volumes | micro cells |
| 10 mm (standard) | Routine UV-Vis, most assays | 10 mm standard cells |
| 20 – 100 mm | Trace analysis, very dilute samples | long-path cells |
Related: Cuvette Care Guide · Path Length Guide · Size Calculator · Path Length Calculator · Brand Alternatives · Contact Scuvette
Need a hand? Our engineers can help you select the right cuvette for your instrument and application — or supply custom optical cells to your drawing. Contact Scuvette →Path length is the distance the light travels through the sample, from the inner face of one window to the inner face of the opposite window. The standard value is 10 mm, or 1 cm.
By the Beer-Lambert law (A = epsilon c l), absorbance is directly proportional to path length. Doubling the path length doubles the absorbance at the same concentration, which lets you tune the signal up or down.
Use a short path for concentrated or strongly absorbing samples that would saturate a 10 mm cell. It lets you measure without diluting, preserving the sample and avoiding dilution error.
Use a long path for very dilute or trace analytes where a 10 mm cell gives too weak a signal. Longer paths amplify the absorbance into a measurable, accurate range.
Enter your sample concentration and target absorbance, and the calculator recommends the shortest path length that keeps the reading in the linear, accurate region, from 1 mm up to 100 mm.