Drybench Calc.
OD600 to cells per mL, as an estimate
An estimate of cells, CFU or microsphere equivalents per mL from an OD600 reading and your own calibrated factor; no factor is built in.
Cells from OD600 (estimate)
Use measured inputs and your protocol’s targets. Save the exact setup or export a free preparation sheet.
No factor is built in. Enter your own k with what it was calibrated against, its source, the instrument and vessel, and the OD range it holds over. Plate readings are never converted to cuvette readings.
From your paired calibration data (optional)
Answer
Estimated cells/mL from OD600: 3.2E9, an estimate from your factor.
- Blank-corrected reading
- 0.4OD600
- Estimate from OD600
- 3.2E9cells/mL
Planned calculation; no performed preparation is recorded.
Calculated setup
| Quantity or basis | Value |
|---|---|
| Blank-corrected reading | 0.4 OD600 |
| Dilution factor | 10 |
| Your factor k | 800,000,000 per mL per OD600 |
| Estimate from OD600 | 3.2E9 cells/mL |
| Lowest calibrated OD600 | 0.05 OD600 |
| Highest calibrated OD600 | 0.6 OD600 |
- Calculated setup only; this is not a performed preparation or measurement.
- An estimate from your calibration, not a count. OD600 measures light scattering. The factor depends on the instrument's optics and path length, the organism, cell size and growth phase, and holds only within the calibrated OD range. Dead cells and debris scatter too.
Illustrative arithmetic only; no biological target or equipment setting is recommended.
Open in the bench sheetThe bench sheet carries these inputs and offers the other calculators.
Worked example
- A reading of 0.45 against a 0.05 blank on a 1:10 dilution, with a factor of 8 × 10⁸ per OD unit from your own calibration: 0.40 × 10 × 8 × 10⁸ = 3.2 × 10⁹ cells/mL, an estimate.
- The factor is yours: what it was calibrated against (cells, CFU or microspheres), its source, the instrument and vessel, and the OD range it holds over. No factor is built in, for any organism.
- A blank-corrected reading of 1.2 against a calibration over 0.05 to 0.6 is refused: dilute and re-measure. Plate readings are never converted to cuvette readings.
- An estimate from your calibration, not a count, and never a viable count; it does not fill the cell seeding calculator.
Method
- Cells from OD600, an estimate from your own calibration factor. Estimate per mL = (OD − blank) × dilution × k, with k, its basis and its calibrated range supplied by you; no default factor (Beal et al. 2020, doi:10.1038/s42003-020-01127-5; Stevenson et al. 2016, doi:10.1038/srep38828).Checked against exact rational arithmetic (Python 3.13.16 fractions) on 14 cases, 9 of them refusals, to nine significant figures; refusals exact (10 October 2026). Every factor in the cases is a stated example of a person's own calibration.
Limits
- For research and education only, and not medical advice: the stock, dilution and buffer calculations here are not for dosing or clinical preparation.
- OD600 estimates use only the factor you supply with its basis, source and calibrated range; readings outside that range are refused, and an estimate is never a count or a viable count.