Keep one basic digital contact thermometer. It is the clearest all-round choice for most households: adults can use it under the tongue or in the armpit, while children under 5 should have their temperature taken in the armpit. A high temperature is usually 38C or above, but symptoms matter as well as the number (NHS adults, NHS children).
Ear thermometers are quick but technique matters. Forehead strips are not accurate. The NHS advises against infrared thermometers, because some do not meet UK regulations. A simple digital stick will do the useful job without asking for Wi-Fi, an account or a committee meeting.
Which digital thermometer should you keep?
What is the best general-purpose thermometer?
A small contact digital thermometer with a clear display, an audible signal and a replaceable or dependable battery is the sensible default. It works for adults and children when used at the right site. Keep its cap and leaflet, because the waiting time, cleaning method, waterproofing and low-battery warning vary by model.
The public GOV.UK Prepare checklist includes a thermometer among example first-aid supplies. One reliable device you know how to use is more useful than several mystery gadgets with flat batteries.
| Type | Best for | Watch out for |
|---|---|---|
| Digital contact stick | Most households; oral or armpit use as directed | Use the correct body site and keep it still until the signal |
| Digital ear thermometer | A quick reading in someone old enough for the probe to fit properly | Poor placement can give a misleading result, especially in babies |
| Contactless infrared thermometer | Not recommended by the NHS for home use | Some do not meet UK regulations |
| Forehead strip | Not recommended for deciding body temperature | It measures skin temperature and is not accurate |
| Old glass mercury thermometer | Do not use | It can break and release glass and poisonous mercury |
The NHS says not to use glass thermometers, infrared thermometers (because some do not meet UK regulations) or forehead strips (because they are not accurate) (NHS).
How to buy a thermometer you can rely on
A thermometer sold for measuring fever is a medical device. The MHRA advises checking for a CE, UKCA or CE UKNI mark, the manufacturer’s address, clear instructions and suitability for the intended user. Read the leaflet before the first ill day, not while somebody is shivering beside you (MHRA).
If you already have an infrared thermometer, the MHRA’s guidance explains what a compliant one must show: the manufacturer, model and batch or lot on the device and packaging. If yours doesn’t, don’t rely on it (MHRA infrared thermometer guidance).
No mark makes technique irrelevant, and the MHRA does not endorse individual products. Buy from a traceable seller, keep the receipt, register the device if offered and report a safety problem through the MHRA Yellow Card scheme.
How to take an adult’s temperature properly
How do I take an oral temperature with a digital thermometer?
Use a digital contact thermometer intended for oral use. The NHS method is:
- Clean the tip with cold water and soap, then rinse it.
- Switch the thermometer on.
- Put the tip under the tongue, towards the back of the mouth.
- Close the lips around it. Do not bite it.
- Keep it in place until it beeps or flashes.
- Remove it and read the display.
Those steps come from the NHS adult fever guidance. Follow the manufacturer’s directions as well. If the instructions differ because your device is designed for another site, use the method in its leaflet.
How do I take an adult’s temperature in the armpit?
Place the clean tip high in a dry armpit, directly against skin. Bring the arm firmly against the body and keep it there until the thermometer signals. Then remove it and read the display (NHS).
Record the number, time and body site if you may need to tell a clinician. If a result looks implausible, check the battery and instructions, then repeat the reading using the same site and method. Do not keep measuring every minute; look at how the person feels too.
How to take a child’s or baby’s temperature
Where should I put the thermometer for a child under 5?
Use a digital thermometer in the armpit. Place the tip at the top of the armpit against skin, close the arm over it and hold the arm gently against the side of the body. Leave it for the time stated in the leaflet; some models beep when ready. Then read the display (NHS).
Do not take an oral temperature from a baby or young child. They may not keep the thermometer safely and correctly in place. The armpit method is the NHS household method for children under 5.
What can make a child’s reading misleading?
A bath, energetic play, a very warm room, lots of clothing, tight wrapping in a blanket or cuddling a hot water bottle can temporarily affect the reading. Let the child cool for a few minutes without making them cold or shivery, then try again (NHS baby guidance).
Ear thermometers can give misleading readings if they are not placed correctly, which is particularly easy with a baby’s small ear canal. Forehead strips show skin temperature, not body temperature. If a reading conflicts with how unwell the child appears, do not let the gadget overrule your concern.
What does the reading mean?
Is 38C a high temperature?
Yes. The NHS usually defines a high temperature as 38C or above for adults and children. Normal temperature varies between people and through the day. An adult who feels hot, cold or shivery may still have a high temperature even if the reading is below 38C (NHS).
For an adult, get an urgent GP appointment or use NHS 111 if a high temperature is not improving or is getting worse despite home care. A thermometer supports a decision; it does not diagnose the cause.
When does a child’s temperature need urgent advice?
Call NHS 111 if a child is:
- under 3 months with a temperature of 38C or higher, or you think they have a high temperature;
- aged 3 to 6 months with a temperature of 39C or higher, or you think they have a high temperature;
- has had a high temperature for 5 days or more; or
- has a high temperature and other signs of illness, such as a rash, or won’t eat, seems unwell or shows signs of dehydration.
Call 999 for danger signs including difficulty breathing, a first fit, a stiff neck, a rash that does not fade when you press a glass against it, blue, grey, pale or blotchy skin, being drowsy and hard to wake, confusion, or not responding as they normally do. See the full, current list on the NHS child fever page.
If you live in Northern Ireland, Scotland or Wales
The thermometer method does not change, but the non-emergency route does. In Scotland, call NHS 24 on 111; in Wales, call NHS 111 Wales on 111; in Northern Ireland, contact your area’s GP out-of-hours service when your GP is closed. Call 999 for a life-threatening emergency (NHS 111 Wales, England and Scotland routes, nidirect).
Store it ready for the day you need it
Clean and dry the thermometer as its leaflet directs, replace the cap and store it with your first-aid supplies, away from heat, damp and children. Check that the display and battery work every few months. Keep a spare battery only if the model uses a user-replaceable one.
While you are checking the cupboard, check medicine dates and return expired or unwanted medicines to a pharmacy. Keep medicines out of sight and reach of children, and ask a pharmacist about anything specific, including suitability and storage (NHS). Keep repeat prescriptions ordered in good time, but order only the usual medicines you need rather than extra packs (NHS trust guidance).
Get ahead (1-2 months before)
- Choose one contact digital thermometer and keep its leaflet with the device (MHRA).
- Practise the correct armpit method for a child under 5 while everyone is well (NHS).
- Test the display and battery and store the device as its manufacturer directs (MHRA).
- Check medicine expiry dates and return unwanted or expired packs to a pharmacy (NHS).
- Order only your usual repeat medicines in good time rather than adding extra packs (NHS trust guidance).
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Sources
- GOV.UK Prepare, Get prepared for emergencies: https://prepare.campaign.gov.uk/get-prepared-for-emergencies/
- NHS, High temperature in adults: https://www.nhs.uk/symptoms/fever-in-adults/
- NHS, High temperature in children: https://www.nhs.uk/symptoms/fever-in-children/
- NHS, How to take your baby’s temperature: https://www.nhs.uk/baby/health/how-to-take-your-babys-temperature/
- MHRA, Medical devices: information for patients: https://www.gov.uk/guidance/medical-devices-information-for-users-and-patients
- MHRA, Infrared thermometers: caution in use: https://www.gov.uk/government/publications/infrared-ir-thermometers-caution-in-use
- NHS, Medicines for babies and children: https://www.nhs.uk/baby/health/medicines-for-babies-and-children/
- Surrey and Borders Partnership NHS Foundation Trust, Only order the medicines you need: https://www.sabp.nhs.uk/our-services/advice-guidance/medicines/only-order-medicines-you-need
- NHS 111 Wales, Calling 111: https://111.wales.nhs.uk/Calling111.aspx
- NHS 111 Wales, Services in England and Scotland: https://111.wales.nhs.uk/aboutus/servicesenglandscotland/
- nidirect, GP out-of-hours service: https://www.nidirect.gov.uk/articles/gp-out-hours-service