How do you calculate the F0 value for an autoclave?

At each temperature reading, compute the lethal rate L = 10^((T − 121.1) / 10), then add up L × the time between readings (this calculator averages neighboring rates with the trapezoidal rule). The total, in minutes, is F0: the equivalent time at 121.1 °C.

What F0 does a 15-minute or 8-minute hold at 121 °C give?

At 121.0 °C the lethal rate is 10^(−0.1 / 10) = 0.9772, so a 15-minute hold gives F0 ≈ 14.66 minutes and an 8-minute hold gives F0 ≈ 7.82 minutes. At exactly 121.1 °C, F0 equals the hold time. These figures cover the hold only; heat-up and cool-down add lethality when included.

What is the F-value at 126.1 °C with a z-value of 10 °C?

The lethal rate is 10^((126.1 − 121.1) / 10) = 10^0.5 = 3.162, so each minute at 126.1 °C is worth about 3.16 minutes at 121.1 °C. A 5-minute hold at 126.1 °C therefore gives F0 ≈ 15.8 minutes.

What F0 value is required for steam sterilization?

It depends on the product and the governing guidance. The Ph. Eur. 5.1.1 reference cycle is at least 121 °C for at least 15 minutes at every load position (F0 about 15). The EMA sterilisation guideline (2019) requires F0 of at least 8 minutes and a hold of at least 110 °C for any terminal steam process. Low-acid canned foods use a minimum botulinum cook of about F0 = 3 minutes (12 × D 0.21 min). The qualified limits for your load always take precedence.

What is the difference between the trapezoidal F0 and Σ L·Δt?

Both approximate the integral of the lethal rate. Σ L·Δt multiplies each reading's lethal rate by its sampling interval, which is how most autoclave and retort controllers accumulate F0 in real time. The trapezoidal rule averages the rates at both ends of each interval. With frequent readings they agree closely; with sparse readings on a steep ramp they can differ, and the gap is a sign the sampling is too coarse.

How do I convert an F-value into log reduction or SAL?

Divide F by the D-value of the target organism at the same reference temperature: log reduction = F ÷ D. Survivors = N₀ × 10^(−F/D). For F0 = 15 minutes and a biological indicator with D121 = 1.5 minutes, the log reduction is 10; starting from 10⁶ spores leaves 10⁻⁴ survivors per unit, a 1-in-10,000 probability of a non-sterile unit.

How long must I hold at 115 °C to reach F0 = 15?

The lethal rate at 115 °C is 10^((115 − 121.1) / 10) = 0.2455, so the hold must last 15 ÷ 0.2455 = 61.1 minutes at the cold spot, ignoring come-up and cool-down. At 118 °C it is 30.6 minutes and at 125 °C 6.1 minutes. The hold-time card and the lethal rate table on this page give other combinations.

What is FH in dry heat sterilization?

FH is the dry-heat equivalent of F0: the lethality of a dry-heat cycle expressed as equivalent minutes at 170 °C with a z-value of 20 °C (USP ). Choose the Dry heat FH preset to calculate it from oven or tunnel temperature data. Depyrogenation uses different references and endotoxin-reduction targets.

What is the F-value in sterilization?

The F-value is the equivalent time in minutes at a reference temperature (Tref) that delivers the same lethality as the actual time-temperature process. It integrates the heat input over the entire cycle so processes with different temperature profiles can be compared on a common scale.

What is F0 specifically?

F0 is the equivalent exposure time at 121.1 °C using a z-value of 10 °C for moist heat. It is one process parameter, not proof by itself that a load is sterile or suitable for release. Qualified cycle limits, load configuration, sensor location, calibration and the validated process still govern interpretation.

The z-value is the temperature interval required for a tenfold change in the D-value. Use the z-value established for the relevant organism, product and process basis. A z-value in °F is an interval, so it equals the °C interval multiplied by 9/5.

What is the D-value and does this calculator use it?

The D-value is the time at a specified temperature required for a 90% (one-log) reduction of a particular microbial population under stated conditions. This tool does not ask for D and therefore does not claim an organism-specific log reduction.

How accurate is the trapezoidal integration?

Accuracy depends on sampling interval, sensor accuracy, sensor location and how closely straight-line interpolation represents the temperatures between readings. Add readings frequently enough to capture heating, holding and cooling transitions; this tool does not assign a universal error percentage.

Can I use Fahrenheit temperatures?

Yes. Switching units converts the reference temperature, z interval and every entered temperature so the physical profile is preserved. The calculated F-value remains equivalent apart from displayed rounding.

Sterilization F Value Calculator

Calculate equivalent exposure time at your reference temperature from a sampled thermal profile. Results are computational support, not process validation or a sterility/release decision.

The F0 value for an autoclave is the equivalent number of minutes at 121.1 °C (z = 10 °C) that a moist-heat cycle delivers: F0 = Σ 10^((T − 121.1) / 10) × Δt.

Process Parameters

Reference Temp (Tref)

Z-value

Temperature Unit

Reference presets

F0 convention: Tref = 121.1 °C and z = 10 °C for moist heat.
Important: Use parameters and acceptance limits from your qualified process. This calculation does not validate a cycle or certify sterility.

Time-Temperature Data Points

Time (min)

Temp (°C)

Time (min) Temp (°C) Delete

No data points yet — add at least 2 unique times to calculate.

Paste data-logger readings

One reading per line: time, temperature (comma, tab, semicolon or space), or temperatures only at a fixed interval. Header lines are skipped.

Interval for temperature-only lists (min)

Results

Add data points and click Calculate to see results.

Log Reduction & Sterility Assurance

Log reduction = F ÷ D, where D is the organism's D-value at the same Tref and z. Survivors = N₀ × 10^(−F/D).

F (min)

D-value (min)

Initial count N₀

The F field is filled from the last calculation. Example values: a biological indicator of 10⁶ spores with D = 1.5 min at 121.1 °C.

Hold Time to Reach a Target F

Minutes at a constant temperature T = target F ÷ 10^((T − Tref) / z), using the Tref, z and unit set above.

Hold temperature (°C)

Target F (min)

F0 Lethal Rate Table (121.1 °C, z = 10 °C)

Lethal rate L = 10^((T − 121.1) / 10): F0 minutes gained per minute at temperature T, and the hold time needed for common F0 targets.

T (°C)	T (°F)	L	Min for F0 3	Min for F0 8	Min for F0 15
100	212.0	0.0078	386	1,031	1,932
105	221.0	0.0245	122	326	611
110	230.0	0.0776	38.6	103	193
112	233.6	0.1230	24.4	65.0	122
114	237.2	0.1950	15.4	41.0	76.9
115	239.0	0.2455	12.2	32.6	61.1
116	240.8	0.3090	9.71	25.9	48.5
118	244.4	0.4898	6.13	16.3	30.6
119	246.2	0.6166	4.87	13.0	24.3
120	248.0	0.7762	3.86	10.3	19.3
121	249.8	0.9772	3.07	8.19	15.3
121.1	250.0	1.0000	3.00	8.00	15.0
122	251.6	1.2303	2.44	6.50	12.2
123	253.4	1.5488	1.94	5.17	9.68
124	255.2	1.9498	1.54	4.10	7.69
125	257.0	2.4547	1.22	3.26	6.11
126	258.8	3.0903	0.97	2.59	4.85
128	262.4	4.8978	0.61	1.63	3.06
130	266.0	7.7625	0.39	1.03	1.93
132	269.6	12.3027	0.24	0.65	1.22
134	273.2	19.4984	0.15	0.41	0.77

Each 10 °C changes L tenfold; each 1 °C changes it by 10^0.1 = 1.259 (about 26%). Times assume the whole load is at T for the full hold.

Reference Conditions and Common F Benchmarks

Use	Tref / z	Benchmark
Moist heat (steam) F0	121.1 °C / 10 °C	Equivalent minutes at 121.1 °C (250 °F); FDA D, z and F definitions
Ph. Eur. 5.1.1 reference cycle	121 °C / 10 °C	≥ 121 °C for ≥ 15 min at every load position (F0 ≈ 15)
EMA sterilisation guideline (2019)	121 °C / 10 °C	Terminal steam processes: F0 ≥ 8 min and hold ≥ 110 °C; holds below 115 °C need extra justification
Low-acid canned food (botulinum cook)	250 °F / 18 °F	12D for C. botulinum: 12 × D_250°F 0.21 min = 2.52 min, conventionally F0 ≥ 3 min; the scheduled process is set by a process authority (21 CFR 113)
Dry heat FH	170 °C / 20 °C	Equivalent minutes at 170 °C (USP <1229.8>); typical dry-heat sterilization runs 160–190 °C

Worked example: come-up and cool-down count

Readings every minute at 100, 110, 115, 118, 120, 121.1, 121.1, 121.1, 120, 118, 115 and 110 °C give lethal rates 0.008, 0.078, 0.245, 0.490, 0.776, 1, 1, 1, 0.776, 0.490, 0.245 and 0.078. The trapezoidal F0 over the 11 minutes is 6.1 min, while the 2-minute plateau alone contributes only 2.0: heating and cooling deliver about two-thirds of the lethality, which is why F0 is calculated from the whole profile, not the hold time.

Sources: EMA guideline on sterilisation · 21 CFR Part 113 · USP <1229.8> Dry Heat Sterilization · Ph. Eur. 5.1.1.

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Quick answer

The F0 value for an autoclave is the equivalent number of minutes at 121.1 °C (z = 10 °C) that a moist-heat cycle delivers: F0 = Σ 10^((T − 121.1) / 10) × Δt. One minute at 121.1 °C adds 1.0 minute of F0; one minute at 111.1 °C adds only 0.1.

Example: 15 minutes held at 121.0 °C: lethal rate 10^((121.0 − 121.1) / 10) = 0.9772, so F0 = 15 × 0.9772 = 14.66 minutes

Add your own time-temperature readings for cumulative F0 per interval, then copy results.

Summary

The F-value expresses a sampled thermal exposure as equivalent minutes at a stated reference temperature. This calculator evaluates lethal rate L = 10^((T - Tref) / z) at each reading, integrates it with the trapezoidal rule and also reports the controller-style sum Σ L·Δt. Presets cover steam F0 (121.1 °C or 121 °C, z = 10 °C), food F0 (250 °F, z = 18 °F) and dry-heat FH (170 °C, z = 20 °C); logger readings can be pasted in bulk. From F and a D-value it gives log reduction and survivors per unit, and it solves the hold time needed for a target F. A computed value must be assessed within a validated, product-specific process.

How it works

Enter the reference temperature (Tref) and the applicable z-value for your validated process basis.
Add at least two unique time-temperature readings, or paste a data-logger export (time, temperature per line, or temperatures at a fixed interval).
The calculator numerically integrates the lethal rate 10^((T - Tref) / Z) over time using the trapezoidal rule.
The result is the F-value in minutes, equivalent to holding at Tref for that duration; the controller sum Σ L·Δt and the minutes at or above Tref are shown alongside.
Enter the organism's D-value and initial count to convert F into log reduction and survivors per unit, or solve the hold time for a target F at a constant temperature.
Compare the result only with the qualified minimum and maximum limits for the specific product, load and cycle.

Use cases

Supporting review of autoclave time-temperature profiles (F0 calculation).
Assessing retort sterilization of canned food products.
Evaluating pasteurization processes for beverages and dairy.
Comparing sterilization efficacy of different temperature profiles.
Academic study of thermal death kinetics and microbial lethality.
Checking numerical integration independently during thermal-process review.
Calculating equivalent sterilization time for irregular heating profiles.
Teaching thermal process engineering concepts interactively.

Frequently Asked Questions

Last updated: 2026-10-09 · Reviewed by Nham Vu