Laboratory Temperature Converter
Laboratory Temperature Converter
Convert between Celsius, Fahrenheit and kelvin, with the storage and incubation temperatures a laboratory actually runs on and why a few degrees of freezer drift matters.
Temperature converter
°C ⇄ °F ⇄ K37 °C, the standard incubation and reference-method temperature
Formula and the fixed points
°C = (°F − 32) × 5 ÷ 9
K = °C + 273.15 · absolute zero = −273.15 °C = −459.67 °F = 0 K
- 9/5
- the ratio of the degree sizes: a Fahrenheit degree is five ninths of a Celsius degree, so 180 Fahrenheit degrees span the same interval as 100 Celsius degrees
- + 32
- the offset between the zero points. It applies to temperatures but NOT to temperature differences: a rise of 10 °C is a rise of 18 °F, not 50 °F
- 273.15
- the offset from Celsius to kelvin. The degree size is identical, so a difference of 1 °C is a difference of 1 K and the kelvin takes no degree sign
- −40
- the one temperature at which the Celsius and Fahrenheit scales read the same number, which makes it a quick sanity check on a conversion
Worked example
37 °C, the standard incubation and reference-method temperature
37 × 9 ÷ 5 = 66.6
66.6 + 32 = 98.60 °F
In kelvin: 37 + 273.15 = 310.15 K
Between 95 °F and 100.4 °F → normal human range
Laboratory temperatures in all three scales
| What it is | °C | °F | K |
|---|---|---|---|
| Liquid nitrogen, vapour phase cell storage | −196 | −320.8 | 77.15 |
| Long-term archive freezer | −80 | −112.0 | 193.15 |
| A −80 freezer that has drifted | −70 | −94.0 | 203.15 |
| Standard laboratory freezer | −20 | −4.0 | 253.15 |
| Refrigerated storage, lower limit | 2 | 35.6 | 275.15 |
| Refrigerated storage, upper limit | 8 | 46.4 | 281.15 |
| Controlled room temperature | 20 | 68.0 | 293.15 |
| Incubation and IFCC reference methods | 37 | 98.6 | 310.15 |
| Complement inactivation | 56 | 132.8 | 329.15 |
| Boiling water at one atmosphere | 100 | 212.0 | 373.15 |
What each storage temperature is for
| Temperature | Used for | What goes wrong if it drifts |
|---|---|---|
| 2–8 °C | Most reagents, calibrators, controls and refrigerated samples awaiting analysis | Above 8 °C shortens reagent and analyte stability; at or below 0 °C the sample may freeze, haemolyse and become unusable for potassium and LDH |
| −20 °C | Short- to medium-term aliquot storage | Auto-defrost freezers cycle well above −20 °C at each defrost, so repeated partial thawing degrades labile analytes even when the mean temperature looks correct |
| −80 °C | Long-term serum, plasma and nucleic acid archives | Drift to −70 °C looks negligible but shortens usable storage life for labile analytes; enzymatic and hydrolytic processes are slowed, not stopped |
| −196 °C | Viable cells, in the vapour phase above liquid nitrogen | Warming above about −130 °C allows ice recrystallisation and kills cells; viability is lost long before anything visibly thaws |
| 37 °C | Incubation, water baths and the IFCC enzyme reference procedures | A water bath running a degree or two low measurably lowers reported enzyme activities |
| 56 °C for 30 minutes | Heat inactivation of complement in serum | Too cool leaves complement active; too hot or too long denatures immunoglobulins and generates aggregates |
The temperatures a laboratory runs on
The three scales differ in two ways only: where they put zero, and how large a degree is. Celsius and kelvin share a degree size and differ by an offset of 273.15, so a temperature difference of 1 °C is a difference of 1 K and the kelvin needs no degree sign. Fahrenheit differs in both respects, its degree being five ninths the size, which is why the conversion carries a multiplication as well as an addition. The offset applies to temperatures and not to differences: a rise of 10 °C is a rise of 18 °F. Absolute zero, −273.15 °C, is the floor of all three, and −40 is the single point at which the Celsius and Fahrenheit scales read the same number.
A laboratory runs on a short list of temperatures, and each is chosen for a reason. Refrigerated storage at 2–8 °C slows degradation without freezing, and the lower limit is there because a frozen whole blood sample haemolyses and takes its potassium and lactate dehydrogenase results with it. Aliquots go to −20 °C for the medium term and −80 °C for archives; cells go to the vapour phase above liquid nitrogen at about −196 °C. Incubation, water baths and the IFCC enzyme reference procedures run at 37 °C, and complement is inactivated at 56 °C for thirty minutes.
Freezer temperature is a continuous variable rather than a pass or fail, which is why a unit that has drifted from −80 °C to −70 °C deserves attention even though ten degrees out of eighty looks small. Freezing does not stop chemistry, it slows it, and the rate falls steeply with temperature, so the difference translates into a materially shorter usable storage life for labile analytes and for the samples a biobank most wants to keep. Frost-free freezers are worse than their mean temperature suggests, because each automatic defrost cycle warms the contents well above the set point.
Blood gas analysers add a subtlety of their own. They thermostat the sample to 37 °C and report what they measured there, whatever the patient’s temperature was. In a hypothermic patient the measured values can be mathematically corrected to the actual body temperature, and doing so lowers the reported carbon dioxide tension and raises the pH. Whether to correct is the alpha-stat versus pH-stat question: alpha-stat manages the uncorrected 37 °C values, pH-stat manages the temperature-corrected ones, and the two lead to different clinical decisions in deep hypothermia. The laboratory’s job is to state clearly which numbers it has issued.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply by 9, divide by 5, then add 32. Body temperature of 37 °C becomes 98.6 °F. Going the other way, subtract 32 first and then multiply by 5 and divide by 9.
How do I convert Celsius to kelvin?
Add 273.15. The degree size is identical in the two scales, so 37 °C is 310.15 K and a difference of 1 °C is a difference of 1 K. The kelvin is written without a degree sign.
Does it matter if a −80 °C freezer drifts to −70 °C?
Yes. Freezing slows chemical and enzymatic degradation rather than stopping it, and the rate rises steeply with temperature, so ten degrees of drift shortens the usable storage life of labile analytes even though the numbers look close.
Why are samples stored at 2–8 °C rather than just cold?
The upper limit slows degradation and microbial growth; the lower limit keeps the sample above freezing. A whole blood sample that freezes haemolyses, which makes potassium, LDH and AST unreportable.
Why do blood gas analysers report at 37 °C?
Because they thermostat the sample to 37 °C and measure it there. For a hypothermic patient the values can be corrected to the actual body temperature, which lowers the carbon dioxide tension and raises the pH — the alpha-stat versus pH-stat question.
Related calculators
References
- Bureau International des Poids et Mesures. The International System of Units (SI Brochure). 9th ed. — the kelvin, the degree Celsius and the relation between them.
- Thompson A, Taylor BN. Guide for the Use of the International System of Units (SI). NIST Special Publication 811 — temperature conversions and the correct use of the kelvin.
- Clinical and Laboratory Standards Institute. Blood Gas and pH Analysis and Related Measurements. CLSI guideline C46 — measurement at 37 °C and temperature correction.