MKT and F0 Value: How to Calculate Them from Temperature Logger Data

Pharmaceutical plants record temperatures all day – in stores, cold rooms, stability chambers and autoclaves. Two numbers turn those readings into decisions: mean kinetic temperature (MKT), which tells you whether storage conditions were acceptable over a period, and the F0 value, which tells you how much lethality a moist-heat sterilisation cycle delivered. Both come straight from logged temperature data. This guide explains what each one means, how it is calculated, with worked examples, and how a data logger such as Tejaxo Logger produces them automatically.

What mean kinetic temperature (MKT) is

Medicines degrade faster at higher temperatures, and the effect is not linear: a few hours at a high temperature can do more harm than many hours slightly below the limit. A simple average hides that. MKT is a single temperature that would cause the same total degradation as the actual, varying temperatures over the period. Because it weights peaks more heavily, MKT is always equal to or higher than the arithmetic average.

The MKT formula

MKT (in kelvin) = (ΔH / R) / −ln[(e^−ΔH/RT1 + e^−ΔH/RT2 + … + e^−ΔH/RTn) / n]

• T1 … Tn are the readings in kelvin (°C + 273.15), taken at equal intervals.
• n is the number of readings.
• ΔH is the activation energy; a value of 83.144 kJ/mol is widely used, which with the gas constant R = 0.0083144 kJ/mol/K gives ΔH/R = 10,000 K.

Subtract 273.15 from the result to get MKT in °C.

Worked example: five readings

A store logged five equally spaced readings: 25, 27, 30, 22 and 26 °C (sample data). The simple average is 26.00 °C. Converting each reading to kelvin, taking e^−10,000/T for each, averaging those five values and applying the formula gives an MKT of 26.35 °C. The 30 °C reading pulls MKT above the plain average – exactly the effect the calculation is designed to capture. In practice a logger uses hundreds or thousands of readings over a month, not five, but the arithmetic is the same.

A cold-room example: one excursion

Now take a cold room meant to stay between 2 and 8 °C. Six equally spaced readings are 4, 5, 6, 5, 4 and 12 °C – the last one during a door left open or a compressor trip (sample data). The simple average is 6.00 °C, comfortably inside the range, and would suggest nothing happened. The MKT is 6.54 °C: still inside the range, but higher, because the 12 °C reading carries more weight. The excursion itself must still be investigated through the alarm record – MKT summarises the period, it does not excuse the event. That is why a logger needs both: alarms for the moment a limit is crossed, and MKT to show the overall thermal exposure of the stock.

MKT, alarms and the batch record

Each of the three tools answers a different question. Alarms answer “did the temperature cross a limit, when and for how long?” and must be acknowledged with a reason. MKT answers “over this month, was the product kept under acceptable conditions overall?” The batch and stock records in the ERP answer “which batches were in that store or that autoclave load at the time?” Together they let quality decide quickly which batches an excursion affected, instead of searching through printouts.

What the F0 value is

In moist-heat sterilisation, what matters is not only the peak temperature but how long the load spent at lethal temperatures. The F0 value expresses the total lethality of a cycle as the equivalent number of minutes at 121.1 °C. A cycle that rises slowly, holds and cools can be compared with any other cycle by its F0.

The F0 formula

F0 = Σ Δt x 10^{(T − 121.1) / z}

• T is the temperature at each reading in °C.
• Δt is the interval between readings in minutes.
• z is the temperature change that alters lethality tenfold; 10 °C is the standard value for moist heat.

A minute at exactly 121.1 °C adds 1.0 to F0; a minute at 111.1 °C adds only 0.1.

Worked example: a ten-minute exposure

An autoclave probe logged one reading per minute (sample data):

Minute	Temp °C	Lethality
1	115	0.245
2	118	0.490
3	120	0.776
4	121	0.977
5	121.5	1.096
6	122	1.230
7	121	0.977
8	121	0.977
9	120	0.776
10	118	0.490
Total		8.04

The cycle delivered an F0 of 8.04 minutes. Your validated process defines the F0 the cycle must reach; the calculation simply shows whether each run met it. Note how the minutes below 121.1 °C still count, but for much less.

Why the readings themselves matter

Both numbers are only as good as the data behind them. Readings must be taken at a fixed interval, from calibrated sensors, without gaps, and stored so they cannot be quietly edited. If a reading is missing or a probe was out of calibration, the MKT or F0 for that period cannot be trusted. That is why the logging system, not a spreadsheet typed up afterwards, should produce the calculation.

How Tejaxo Logger does it

Tejaxo Logger is a Windows program that reads temperature and process instruments over RS-485 or RS-232 using Modbus RTU and logs every reading, with a minimum scan and save interval of 10 seconds. It shows live values and alarms, downloads readings stored in data-logger instruments, and produces trend graphs, data reports with minimum, maximum and average, alarm and audit-log reports, and MKT and F0 calculations, with printing with signatures and Excel export. Security features include individual logins, access rights per command, password ageing, automatic log-off and a full audit trail designed to support 21 CFR Part 11 requirements.

Tejaxo Logger is part of Tejaxo Automation and is linked to Tejaxo ERP, so a pharmaceutical plant can keep batch, expiry and quality records in the ERP and the environmental and sterilisation data in the logger – see ERP for pharmaceutical manufacturers.

Common mistakes

• Reporting the average instead of MKT. The average under-states the effect of temperature peaks.
• Uneven reading intervals. Both formulas assume equal spacing; gaps distort the result.
• Mixing °C and kelvin. MKT must be calculated in kelvin.
• Wrong reference values. Use the ΔH, z and reference temperature your procedures specify, and use the same values every time.
• Calculating by hand from printouts. Retyped data cannot be audited; let the logging system calculate from the stored readings.

Next step

See Tejaxo Logger reading your instruments and producing MKT and F0 reports, alongside batch and expiry control in Tejaxo ERP. Book a free demo.

Frequently asked questions