Microbiology
Sterilization (F₀) Calculator
Converts a heat-sterilisation hold time and temperature into F₀ — the equivalent minutes at the reference temperature.
F₀ value
Enter the hold time in minutes (and check the temperature).
Process parameters
Temperature held during exposure; autoclaves run 115–134°C.
Hold time at that temperature.
°C rise that makes kill 10 times faster.
F₀ is defined at 121°C.
Try an example
F₀ values per minute
Lethality of one minute at each temperature (z = 10°C).
| Temp (°C) | F₀ (min) | Application |
|---|---|---|
| 100 | 0.008 | Pasteurization |
| 110 | 0.077 | Low‑temp |
| 115 | 0.245 | Pharmaceuticals |
| 121 | 0.975 | Standard |
| 125 | 2.448 | HTST |
| 130 | 7.743 | Flash |
Sterilization standards
Bands used for the result: ≥ 12 commercial sterility · 6–12 medical sterility · 3–6 food industry standard · below 3 pasteurization level.
F₀ = t × 10^((T − Tref) ÷ z)
t = time at temperature (min), T = process temperature (°C), Tref = reference temperature (121°C for F₀), z = the temperature change that alters the D-value (decimal reduction time) by a factor of 10 — 10°C for the sterility indicator B. stearothermophilus.
10^((T − Tref) ÷ z) is the lethal rate: how many minutes at the reference temperature one minute at T is worth. At 131°C with z = 10, each minute counts as 10.
Common questions
Because kill rate rises ten-fold for every z degrees. With z = 10°C, 134°C is 1.3 z-values above 121°C, so each minute is worth about 20 minutes at 121°C — 3 minutes gives an F₀ near 60.
10°C for most steam sterilisation work, as it describes Geobacillus (B.) stearothermophilus spores used as biological indicators. 12°C is sometimes used for C. botulinum in food processing; 8°C for some thermophiles.
No. F₀ is minutes of equivalent heating. Divide F₀ by the organism's D₁₂₁ value to get the number of log reductions it delivers — for spores with D₁₂₁ = 1 min, F₀ = 12 gives 12 logs.
Only as an approximation. Validated cycles integrate the lethal rate over the whole measured temperature profile, minute by minute, from a probe in the load.
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