Geratherm® basal: The world’s only analogue basal thermometer

For natural family planning and conscious cycle observation, with a dual Celsius and Fahrenheit scale

Basal body temperature is the lowest body temperature at rest, measured right after waking. Across the cycle it follows a characteristic pattern, and the Geratherm® basal captures these subtle changes. Unlike a fever thermometer that covers a wide range up to 42 °C (107.6 °F), it shows only the narrow band around your wake-up temperature, from 35.6 °C (96.08 °F) to 38.4 °C (101.12 °F). On that short stretch the tenths of a degree sit further apart and are easier to read. The scale is printed in both Celsius and Fahrenheit, and the thermometer works purely analogue with no battery, app or cloud.

Precise & analogue

The Geratherm® basal measures to 0.1 °C (0.18 °F). Its scale shows both Celsius and Fahrenheit and covers only the band around your wake-up temperature, so even small changes are easy to read, enlarged further by the magnifier sleeve.

Sustainable & independent

Mercury-free, with no battery, app or cloud. The glass thermometer can be reused without limit, is fully recyclable and comes with a ten-year warranty.

For fertility & cycle monitoring

Measured daily, your wake-up temperature helps narrow down the fertile days and read your cycle over months. An aid for cycle observation, not a contraceptive.

Made in Germany

Made from special thermometer glass in Germany, in our own production. The sealed glass body is hygienic, easy to clean and suitable for allergy sufferers. MDR-compliant.

Precise & analogue

The Geratherm® basal measures to an accuracy of 0.1 °C (0.18 °F). Unlike a fever thermometer that reaches up to 42 °C (107.6 °F), it shows only the narrow band from 35.6 °C (96.08 °F) to 38.4 °C (101.12 °F) around your wake-up temperature. On that short stretch the tenths of a degree sit further apart, so the small temperature steps of your cycle are much easier to read. The scale is printed in both Celsius and Fahrenheit, so you can read it in whichever unit you prefer, and the storage case with magnifier effect enlarges it further. The thermometer keeps the highest reading until you reset it, so you can read it calmly after measuring instead of catching the exact moment.

Geratherm® basal analogue glass basal thermometer in the storage case with magnifier effect; the magnifier enlarges the scale and the pink Galinstan measuring liquid for easier reading.
Badge "10 Years Warranty" – EU Compliant Medical Product, Geratherm® basal.

Sustainable & independent

No battery, no app, no cloud: there is nothing to charge or pair, and no data that could end up anywhere. The measuring liquid is the non-toxic, mercury-free Galinstan®, the liquid metal developed by Geratherm as a replacement for the mercury used in the past. The glass thermometer is BPA-free, can be reused without limit and is fully recyclable, and it is made from 95 % German-sourced materials. We back its function with a ten-year warranty. Stored properly, the basal will last you a lifetime.

For fertility & cycle monitoring

The Geratherm® basal supports natural family planning and getting to know your own cycle. Measuring daily and recording your values, over time you will see a reliable pattern: the low temperature in the first half of the cycle, a rise of 0.2 to 0.5 °C (0.36 to 0.9 °F) after ovulation, and the higher level that lasts until the next cycle. From this pattern you can narrow down your fertile days.

 

It usually takes about three cycles before your personal pattern is clearly recognisable. After that your cycle is easy to read, whether for family planning, conscious cycle observation or simply to understand your body better. Record everything in a cycle chart or a health or cycle app of your choice. Please note: the basal is an aid for cycle observation and not a contraceptive.

Chart showing the biphasic basal body temperature curve over a 28-day cycle: low temperature in the follicular phase, a rise of 0.2 to 0.5 °C (0.36 to 0.9 °F) after ovulation around day 14, and an elevated high phase in the luteal phase. Scale shown in both Celsius and Fahrenheit.
Production of the Geratherm® basal thermometer at the Geratal site in Thuringia, Germany. An employee loads a production line with precision capillaries from the in-house glass production.

Made in Germany

The Geratherm® basal is produced in Geratal, Thuringia, a region where glass thermometers have been made for over 120 years. The glass tube and the precision capillary come from the Geratherm group’s own glass production; you can recognise the Ilmatherm I-860 thermometer glass by the three white stripes on the scale.

 

The sealed glass body is free of metals and plastics, which makes it hygienic, easy to clean, safe to disinfect and suitable for allergy sufferers. Every thermometer is calibrated and final-inspected before it leaves production.

How to measure

  1. Measure in the morning right after waking, before getting up, and ideally always at the same time.
  2. Beforehand, bring the measuring liquid below 36 °C (96.8 °F) using the reset aid.
  3. Choose one measurement site (oral, vaginal or rectal) and keep to it throughout the cycle.
  4. Measure for the same length of time every morning, at least four minutes. Only a consistent measuring time makes your readings comparable.

  5. Read the value and record it. It stays until you reset the thermometer, so you can note it without rushing.

     

Tip: At least five hours of sleep, and do not eat, drink or smoke before measuring. Clean the thermometer before and after each use.

Hand holding the Geratherm® basal analogue glass basal thermometer with the storage case and magnifier effect; the magnifier enlarges the scale and the pink Galinstan measuring liquid.

Geratherm® basal - The storage case with built-in magnifier

Geratherm® basal analogue glass basal thermometer fully inside the storage case with magnifier effect; the magnifier enlarges the temperature scale and the pink Galinstan measuring liquid.

With its special storage case, the Geratherm® basal is even easier to read. After measuring, place the thermometer in the insert and slide it into the case. The built-in magnifier enlarges the scale and helps you read the result.

 

Hand holding the Geratherm® basal analogue glass basal thermometer in the reset aid; a flick of the wrist returns the Galinstan measuring liquid below the 36 °C (96.8 °F) mark before the next measurement.

How to reset the measuring liquid

Before each measurement the measuring liquid should be below 36 °C (96.8 °F). Place the thermometer in the enclosed reset aid and hold it by the handle between thumb and index finger. Shake it with loose movements from the wrist, tip pointing down, until the liquid drops below the 36 °C (96.8 °F) mark.

 

Important: unlike the old mercury, Galinstan® cannot be reset with cold. So do not put the thermometer in the fridge or hold it under cold water; this will not bring the liquid down. Make sure there are no objects nearby, such as a table or chair, that the thermometer could hit while you shake it.

Technical Data

Measuring range 35.6 °C to 38.4 °C (96.08 °F to 101.12 °F)
Measurement accuracy ± 0.1 °C (± 0.18 °F)
Measurement resolution 0.1 °C (0.1 °F)
Intended purpose Analogue basal thermometer for cycle monitoring
Measuring locations vaginal, rectal, oral
Storage conditions -15 °C to 39 °C (5 °F to 102.2 °F)
Please refer to the instructions for use for full technical data.

In the box

Basal thermometer, protective case, storage case with magnifier effect, reset aid, instructions for use

ieferumfang des Geratherm® basal: analoges Basalthermometer aus Glas, Schutzhülle, Aufbewahrungshülle mit Lupeneffekt und Rücksetzhilfe.

Questions and answers

Measure in the morning right after waking, before getting up, and ideally always at the same time. You should have slept for at least about five hours, ideally without getting up in the last hour. Measure for at least four minutes, always the same length of time, and keep to one measurement site (oral, vaginal or rectal) throughout the cycle. Only consistent conditions make the fine differences comparable.

 

No. The Geratherm® basal measures completely independently of any app or battery. How you record your values is entirely up to you: in a health or cycle app of your choice, in a printed cycle chart or by hand. You can use any app you like, but you don't have to. There is nothing to charge or pair, and no data you have to store anywhere.

Look straight at the scale from the front and turn the tube slightly until the column is clearly visible. The storage case with magnifier effect enlarges the scale. Because the highest value is retained until you reset the thermometer, you can read it calmly after measuring without having to catch the exact moment.

The fine silver line is the thermometer's calibration mark and therefore a quality feature, not a defect. Because each scale is aligned to this mark by hand, it can look slightly different from one thermometer to the next.

It works purely analogue and is calibrated to EN 12470-1, with an accuracy of ± 0.1 °C (± 0.18 °F). The reading stays accurate over the years and does not shift, whereas electronic sensors can become less accurate over time. No battery that goes flat, no software that becomes outdated. And the scale shows both Celsius and Fahrenheit.

Clean it before and after each measurement with water (not above 39 °C / 102.2 °F) and mild soap or a suitable disinfectant. The sealed, smooth glass body is fully waterproof and can be cleaned and disinfected safely. Please do not boil it.

Yes. The sealed glass body is free of metals and plastics, so sensitive skin does not come into contact with problematic materials.

No need to worry: the measuring liquid Galinstan® is non-toxic and mercury-free. Unlike old mercury thermometers, there is no risk of poisoning — for people or pets. No hazardous vapours are released. Brief skin contact is harmless; simply wash the area with soap and water afterwards.

The only precaution concerns metals: Galinstan® bonds with many metals and can attack them, particularly aluminium. Do not use metal tools to collect the liquid, and do not let it come into contact with metal surfaces, cutlery or jewellery.

Here is what to do: carefully collect the glass shards first. Unlike mercury, Galinstan® does not form droplets but smears easily across surfaces. Pick up the silvery liquid with a paper towel or a piece of card; remove any remaining traces with soapy water or a standard household cleaner or scouring agent. This works most easily on smooth surfaces such as tiles or glass. Dispose of the collected liquid together with the glass shards in your household waste — not down the drain. Please do not continue to use a damaged thermometer.

It is intended for cycle observation in women of childbearing age. It is not suitable during menopause or under hormonal treatment, such as hormonal contraception, because there is then no natural cycle pattern.

With proper use, a lifetime. The glass thermometer does not wear out and measures just as accurately after years. We back this with a ten-year warranty.