OD600 Calculator

How to convert OD600 to cells per mL

1. Type the OD600 reading and the dilution factor if you diluted the culture to read it.
2. Choose the organism, or type your own cells per mL at an OD600 of 1.
3. The cells per mL appear. Type a target OD and final volume to see how much culture and fresh medium to mix.

Frequently asked questions

How accurate is the cell count?

It is an estimate. The common rules of thumb are about 8 × 10⁸ cells/mL at OD600 1 for E. coli and 3 × 10⁷ for yeast, but the real factor depends on the spectrophotometer and the strain, so calibrate with a plate count for exact work.

Why dilute before reading?

Above an OD of about 1, readings stop rising in proportion to the cell density. Dilute the culture so the reading is between 0.1 and 1, and type the dilution factor.