Thermometer for a child under five: choose the right type

Your child feels hot, and the drawer holds a digital stick, a room dial and an infrared gun bought for radiators. They may all show degrees Celsius, but they do not measure the same thing. For a thermometer for a child under five, the NHS parent method is a digital thermometer in the armpit. The room dial measures air. The surface gun measures the surface in its spot.

A plausible number can still answer the wrong question. This guide separates the three jobs and sets out the NHS armpit reading. It summarises NHS and NICE guidance as used in October 2026 and does not replace a medical assessment. A qualifying purchase can earn us a commission at no extra cost to you. Featured listing figures are amazon.co.uk prices and ratings from 15 October 2026. Nothing here was lab-tested.

In short

For a child under five, use a clinical digital thermometer in the armpit, hold the arm against the body and follow the instructions until the reading finishes. The NHS says 38°C or more is usually a high temperature, but age and symptoms decide what you do next. Buy a separate room thermometer for air and a purpose-made infrared thermometer for non-clinical surface checks.

The NHS method for a child under five

NHS parent guidance says to use a digital thermometer in the armpit. Place the tip high in the armpit, hold the child's arm against their body, and keep it there for the time in the instructions. The NHS says this is usually about 15 seconds or until the device beeps. The leaflet with your model decides when that model has finished.

If the child has just had a bath or been wrapped tightly in a blanket, wait a few minutes, because either can affect the reading. The NHS puts a normal temperature around 36.4°C, and it can vary, so a small difference is not a diagnosis. The fever threshold on that page is 38°C or more.

You need a clinical digital thermometer whose instructions include underarm use. The thermometer comparison separates body sticks from room and fridge instruments. Its top pick, on score then review count, is the femometer DET-306 at about £14.99, 4.5 from 20,571 ratings: a no-touch forehead thermometer with object and room modes. A forehead scan is a different site from an armpit, so it does not replace the NHS method.

Taking a calmer, repeatable reading

Have the thermometer and its instructions ready before you move the child. Use the same position each time, with the sensor on skin rather than clothing. If it slips or shows an error, start again. Note the number, the time and the method if you speak to NHS 111. How the child looks, breathes, drinks and responds still matters.

Why the measuring site matters

A thermometer senses temperature at one site, with a method it was designed for. An armpit stick, an ear thermometer and a forehead product are not interchangeable because the screens use the same unit. Underarm, ear or forehead on the instructions is how that result should be read. A site the manufacturer does not specify can look precise without being meaningful.

The NHS warns that ear thermometers can mislead when the tip is not positioned correctly, more likely in babies because their ear holes are small. Forehead strips show skin temperature rather than body temperature. That warning is a reason to stay with the parent method when you do not know the device or the site.

Never use a mercury glass thermometer. The NHS says not to use one, and to get medical help immediately if a child is exposed to mercury. A digital stick still needs a working battery, a clean sensor and readable instructions before an ill child needs it.

What NICE guidance does and does not say

NICE NG143 is written for healthcare professionals assessing fever in children under five. For babies under 4 weeks it specifies an electronic thermometer in the axilla, meaning the armpit. From 4 weeks to 5 years, the listed professional options are an electronic or chemical-dot thermometer in the axilla, or an infrared tympanic thermometer in the ear.

That professional list does not licence a non-contact forehead device because a listing shows a baby, and it does not cover a workshop gun ranged for hot machinery. NICE says professionals should not routinely use oral or rectal routes from birth to 5 years, and it calls forehead chemical thermometers unreliable.

At home, the NHS page directs you to the digital armpit method for a child under five. A clinician's ear instrument is a defined device with a placement method. That is not evidence that a catering or radiator gun is the same tool.

An NIHR method-comparison study in children aged 5 and under found that non-contact forehead devices could disagree with electronic axillary or infrared tympanic readings by more than 1°C. That is not a NICE ban. It is a reason to keep the method and the site next to the number.

A room or greenhouse thermometer reads air

A wall dial, window thermometer, wireless room sensor or greenhouse max-min thermometer answers one question: what is the air temperature here? It can compare rooms, show whether a greenhouse cooled overnight, or show how sun warms a sensor. It is not measuring a child's body.

Placement still changes the air reading. A unit beside a radiator, in a sunny window or on a warm wall shows that spot, not the air where you sit. In a greenhouse, a simple dial shows the present temperature, while a max-min model records the extremes between resets. Neither becomes a clinical thermometer.

Room air and body temperature are different jobs. A warm bedroom is not a fever, and a body stick is the wrong tool for greenhouse frost unless its instructions cover air temperature. Keep the clinical thermometer, its case and its leaflet in the medicine cupboard, and check the battery before a night-time reading. Put the room or greenhouse instrument where it samples representative air.

An infrared surface gun is a third product

An infrared surface gun reads the patch of surface inside its measuring spot. It can compare radiators, find a cold area on a wall, or check other non-clinical surfaces within its stated range. A range of hundreds of degrees, common on cooker and engine models, is not evidence of clinical suitability.

The laser on many guns is an aiming aid, not the sensor. The device averages a spot that grows with distance, and the result is the visible surface, not an underarm site. Sweat, a recent wash and the room air also change a forehead, so a workshop gun does not carry out the NHS method.

A purpose-made no-contact forehead thermometer is a different product from a workshop gun, and it still depends on method and site. A body, object or room switch changes how the sensor reads the signal. That split is set out on forehead thermometer or temperature gun. For a child under five, use the NHS digital underarm method.

When to call 111 or 999

The NHS says to call 111 if a baby under 3 months has 38°C or higher, or if a baby aged 3 to 6 months has 39°C or higher. Seek advice too if a high temperature lasts 5 days or more, the child is not their usual self, looks dehydrated, or has a rash or other signs described on the fever page.

Use the current NHS fever page for the full criteria. It lists 999 red flags including a stiff neck, a rash that does not fade when pressed, a first fit or seizure, and difficulty breathing. When the child's condition meets an emergency description, do not wait for a preferred thermometer.

When you call, say the child's age, the number, where you measured it and which thermometer you used. Mention a recent bath or tight wrapping, and any change in breathing, alertness, drinking, urine or rash. A room reading or a surface-gun result is not an underarm temperature. This article does not restate medicine doses. Follow NHS advice and a clinician or pharmacist.