How to Use an Infrared Thermometer: Steps, Conditions and Common Errors

General product and use information only, not medical advice. It does not interpret a reading or replace a clinician or your device’s instructions for use (IFU).

To use a non-contact infrared thermometer, let it settle in the room where you will measure, aim the sensor at a clean, dry, uncovered forehead from the distance your IFU specifies, keep the person still, and read the display. Most wrong readings come from the setup rather than the button press: room conditions, sweat, headwear, and a device that has just come in from the cold. The FDA gives the room conditions as numbers, and a 2021 metrology best-practice guide adds timing rules. This page collects both.

What you need

• A non-contact infrared (forehead) thermometer and its IFU. The IFU sets the measuring distance, the button sequence and the cleaning method for your model. Where this page and your IFU differ, follow the IFU.
• A room that is, per the FDA, draft-free, out of direct sun and away from radiant heat sources, with an environmental temperature between 60.8 and 104 °F (16 to 40 °C) and relative humidity below 85 percent.
• Time: the FDA advises placing the thermometer in the testing environment or room for 10 to 30 minutes before use. The metrology guide says the thermometer should thermalize for about 15 minutes.
• A person who can stay still, with a clean, dry forehead that is not covered.

For how infrared devices compare with other thermometer types, see what a medical thermometer is. For ear and forehead use on infants by age, see the infant digital thermometer guide.

Steps

1. Acclimatise the device. Leave it in the room for the time above. Do not hold it in your hand for a long time during the measurement (metrology guide).
2. Prepare the forehead. It should be clean, dry and unblocked. Remove hats, hair, headbands and head covers from the measuring site, and avoid facial cleansing products and sweat or face creams on the skin (FDA; metrology guide).
3. Let the person settle. The guide says to wait at least 10 minutes after the head covering is removed, and at least 10 minutes after coming in from outside. It also advises against measuring right after showering or swimming.
4. Position the sensor. Hold the sensing area perpendicular to the forehead. The distance is specific to each device (FDA); the metrology guide describes it as typically a few centimetres, with the measured target at least twice the manufacturer’s specified field of view. Use the range stated in your IFU.
5. Keep still and do not touch the sensor. The FDA asks that the person remain stationary during measurement and that nobody touch the sensing area.
6. Take the reading as your IFU describes (button sequence, display mode, whether it is a direct or adjusted mode).
7. Repeat with a gap. If you measure again, wait a minimum of 30 seconds between two measurements (metrology guide). For a trend, always measure at the same place on the forehead.
8. Clean as the IFU says. The FDA notes that most of these devices should never be immersed in water or other liquids.

What can go wrong

The FDA states plainly that improper use may lead to inaccurate temperature measurements. The 2021 best-practice guide also says non-contact methods are in general less accurate than contact thermometers, because of emissivity, the environment and the optics.

Problem	What the sources say to do
Draughts, direct sun, radiant heat, dust	Move to a draft-free spot out of direct sun and away from heat sources (FDA). The metrology guide also advises against air-conditioner drafts and dusty environments.
Device just came from a different temperature	Let it acclimatise in the room for 10 to 30 minutes (FDA) or about 15 minutes (metrology guide).
Sweat, creams, make-up, hair or a hat on the forehead	Clear and dry the site; wait at least 10 minutes after removing a head covering (metrology guide).
Person just came in from outside, or just showered or swam	Wait at least 10 minutes after coming in from outside; avoid measuring right after showering or swimming (metrology guide).
Glasses frames, some tattoos, piercings	The guide lists these as possible sources of distortion; measure a clear area.
Rapid repeat readings	Wait at least 30 seconds between measurements (metrology guide).
New or replaced battery	Wait, usually at least 10 minutes, for the device to stabilise (metrology guide).
Device dropped, wet, left in strong sun, or exposed to extreme temperature, humidity or strong electromagnetic fields such as MRI	The guide recommends checking it against a known traceable reference before relying on it. It recommends the same check after a manufacturer-specified period of routine use. See what calibration is and how calibration intervals are set.
Temporal-artery model with covers	Use the supplied covers, and make sure a cover does not block the field of view (metrology guide). If no covers are prescribed, keep the optics clean.

When to get professional help

A thermometer reading is one piece of information, and what it means for a person’s health is a decision for a clinician, not for this page or the device. If you doubt a reading, the metrology guide advises waiting several minutes and repeating it, or using an independent clinical method. If a device keeps giving readings you doubt, or has been dropped, soaked or otherwise stressed, have it checked against a traceable reference or replaced per the manufacturer’s instructions. In a clinical setting, thermometry sits in the wider point-of-care diagnostic station workflow, and facility policy governs which method is used.

FAQ

How far from the forehead should an infrared thermometer be held?

It depends on the device. The FDA says the distance between the thermometer and forehead is specific to each model, so follow your IFU. The metrology guide describes the distance as typically a few centimetres.

How long should I wait between readings?

A minimum of 30 seconds between two measurements (metrology guide, 2021).

Can I measure right after coming in from outside?

The guide advises waiting at least 10 minutes after coming in from outside before measuring, and at least 10 minutes after removing a hat or head covering.

Why does my reading change from one attempt to the next?

Room conditions, sweat or products on the skin, headwear, distance and angle, and the device’s own temperature all affect readings. The FDA warns that improper use can give inaccurate measurements, and the metrology guide notes that non-contact methods are generally less accurate than contact thermometers.

How do I clean it?

Follow the Cleaning and Disinfecting section of your product instructions. The FDA notes most non-contact infrared thermometers should never be immersed in water or other liquids.

Where can I find thermometers and monitoring equipment?

Browse diagnostic and monitoring equipment.

Sources

• FDA, Non-Contact Infrared Thermometers, content current as of 03/06/2026; checked 2026-10-30.
• Best Practice Guide: Use of Infrared Forehead Thermometers to Perform Traceable Non-Contact Measurements of Human Body Temperature, 3rd version, May 2021, prepared by national metrology institutes (including NPL, LNE-CNAM, INRiM, NIM); checked 2026-10-30. It references ISO 80601-2-56:2017 and ASTM E1965-98 for instruction content.
• Your device’s manufacturer IFU, which governs distance, button sequence and cleaning for your model.