Mean kinetic temperature (MKT) is the single, steady temperature that would cause the same total chemical degradation of a product as the real, fluctuating temperatures it was stored at. Health Canada's GUI-0069 defines it the same way: the calculated temperature at which the total degradation over a period equals the sum of the degradations at each of the temperatures the product saw. It is not an average. MKT weights warm readings far more than cool ones, because degradation speeds up exponentially as the temperature rises.
Why a plain average is misleading
Picture a pharmacy stockroom that sits at 20 °C (68 °F) all day, until the air conditioning fails for four hours and the room reaches 35 °C (95 °F). The average of the 24 hourly readings is 22.5 °C (72.5 °F), which looks comfortably inside a "store at 15 to 25 °C (59 to 77 °F)" label. But reaction rates rise exponentially with temperature, so those four hot hours did far more damage than the average suggests. MKT puts a number on that.
The MKT formula
MKT comes from the Arrhenius equation. For n readings taken at equal intervals:
MKT = (ΔH/R) ÷ −ln[ (e−ΔH/RT1 + e−ΔH/RT2 + … + e−ΔH/RTn) ÷ n ]
- T1 … Tn: each reading in kelvin (°C + 273.15).
- ΔH: the activation energy of the degradation reaction. The usual default is 83.144 kJ/mol, used when no product-specific value is known.
- R: the gas constant, 8.3144 J/(mol·K). With the default ΔH, ΔH/R is 10,000 K, which keeps the arithmetic simple.
- The result is in kelvin: subtract 273.15 for °C, then multiply by 1.8 and add 32 for °F.
The readings must be evenly spaced, like the fixed recording interval of a data logger. If they are not, each reading has to be weighted by the time it stands for.
MKT in Excel: one formula
Paste your readings in °C into column A, one per row, starting at A2. For 24 readings (A2:A25):
=10000/(-LN(AVERAGE(EXP(-10000/(A2:A25+273.15)))))-273.15The result is the MKT in °C. Change A2:A25 so it covers your readings exactly: an empty cell inside the range counts as a 0 °C reading. In Excel 365 the formula works as typed; in older versions, confirm it with Ctrl+Shift+Enter. In Google Sheets, wrap it in ARRAYFORMULA( ). If your readings are in °F, use this version, which also returns °F:
=(10000/(-LN(AVERAGE(EXP(-10000/((A2:A25-32)/1.8+273.15)))))-273.15)*1.8+32Worked example
Take the stockroom above: 24 hourly readings, 20 at 20 °C (68 °F) and 4 at 35 °C (95 °F).
- Convert to kelvin: 20 °C = 293.15 K and 35 °C = 308.15 K.
- Weight each reading: e−10,000/293.15 = 1.532 × 10−15 and e−10,000/308.15 = 8.061 × 10−15. One hour at 35 °C counts about 5.3 times as much as one hour at 20 °C.
- Average the weights: (20 × 1.532 + 4 × 8.061) × 10−15 ÷ 24 = 2.620 × 10−15.
- Take the natural log: ln(2.620 × 10−15) = −33.576.
- Divide: 10,000 ÷ 33.576 = 297.84 K, which is 24.7 °C (76.4 °F).
The arithmetic mean is 22.5 °C (72.5 °F). The MKT is 24.7 °C (76.4 °F): about 2.2 °C (3.9 °F) higher, and close to the top of a 15 to 25 °C (59 to 77 °F) label.
MKT vs the average, minimum and maximum
MKT does not replace your limits. A product can have an acceptable MKT and still have spent hours above its maximum, and a single MKT figure does not say when an excursion happened. That is why a storage record keeps the minimum, the maximum and every excursion, and MKT, where it is allowed, only sums up the overall thermal stress of a period.
When MKT is not appropriate: GUI-0069
In Canada, Health Canada's GUI-0069 guidelines for environmental control of drugs during storage and transportation allow MKT in monitoring only when it is used in line with a recognized pharmacopoeia, with a written procedure for when MKT is appropriate and how it is calculated. Section 5.1 also lists cases where MKT may not be appropriate:
- liquids or suspensions that can change phase;
- products that need refrigeration or freezing;
- biologics;
- cases where data show that temperature excursions affect product quality.
Vaccines are biologics kept in a fridge or freezer, so for a vaccine fridge at 2 to 8 °C (36 to 46 °F), an MKT figure is no substitute for the minimum, maximum and excursion record your immunization program asks for. Our guide to vaccine fridge temperature logs and alarms explains what that record should hold.
MKT in temperature mapping
A temperature mapping study places loggers across a storage area to find its warmest and coldest spots. For a room-temperature area, you can work out the MKT at each position from its exported readings with the formula above, alongside the minimum, maximum and average, which shows where heat stress builds up. For a fridge or freezer, the same GUI-0069 limits apply, so rely on the minimum, the maximum and the time out of range at each position. See our temperature mapping page.
Getting your readings out of MaxLinc
MaxLinc loggers record at a fixed interval, which is what the formula needs. Export the readings to Excel from the app (on WiFi, the free Standard tier keeps a raw Excel download of the last 45 days; Premium, included for each device's first year, adds full history and reports in Excel or PDF), paste them into column A and use the formula above. For pharmacy and clinic fridges, the EDGE Pharma One WiFi (one buffered, NIST-traceable probe) and the EDGE Pharma Two WiFi (two probes, for two fridges side by side) keep that record with Vaccine Temperature and Min/Max/Average Daily reports, and alarm your team when a reading leaves your range. See the full setup for pharmacies and clinics, and if FDA rules apply to your records, read what a 21 CFR Part 11 data logger can and cannot provide.
Quick answers
What does MKT stand for?
Mean kinetic temperature: the single, steady temperature that would cause the same total degradation as a product's real, varying storage temperatures over a period.
Is MKT the same as the average temperature?
No. MKT weights warm readings exponentially, so it is always equal to or higher than the arithmetic mean of the same readings. The more the temperature swings, the bigger the gap.
What activation energy should I use?
83.144 kJ/mol is the usual default when the product's stability data give no specific value. Use the value your written MKT procedure names.
Can I use MKT for a vaccine fridge?
Health Canada's GUI-0069 says MKT may not be appropriate for products that need refrigeration or freezing, or for biologics. For a vaccine fridge, keep the twice-daily current, minimum and maximum record and investigate every excursion, as your immunization program asks.
Sources
Last updated: