Infrared Thermometers: Care & Use Tips

Here are answers to some common questions asked about infrared thermometers,

Can I check my grill temp with an infrared thermometer?

If you aim an infrared thermometer at a porous surface like a grill or grate, it will factor in the surface temp of whatever surfaces are visible through the holes of the grill or grate when calculating a final temperature for your reading.

To accurately measure the temperature of a porous grate or grill, place a solid surface like an iron plate or skillet on the grill, let it come to temperature, and measure the plate or skillet. Spray a little cooking oil on the plate or skillet to ensure proper emissivity.


What is emissivity?

Emissivity is a measure of a material’s ability to emit infrared energy. It is measured on a scale from just above 0.00 to just below 1.00.

Generally, the closer a material’s emissivity rating is to 1.00, the more that material tends to absorb reflected or ambient infrared energy and emit only its own infrared radiation. Most organic materials, including the byproducts of plants and animals, have an emissivity rating of 0.95.

Check your infrared thermometer to see if it has adjustable emissivity settings as a feature. Then, check your target material against this ThermoWorks Emissivity Chart.


Can I check my meat or other foods for doneness with an infrared thermometer?

Since infrared thermometers only measure surface temperatures, they are not very effective at gauging the doneness of foods. Use an instant-read thermometer – such as the Thermapen Mk4 – for this.

When using an infrared thermometer with liquids like soups and sauces, be sure to stir vigorously before taking a measurement to more closely approximate the internal temperature of the liquid. Be aware that steam, even when a liquid is not boiling, can condense on your thermometer and affect the accuracy of your measurements.


Can infrared thermometers see through glass or clear plastic?

Infrared thermometers do not “see through” glass, liquids, or other transparent surfaces even though visible light (like a laser) passes through them—i.e. if you point an IR thermometer out a window, you will be measuring the surface temperature of the window itself.


Do infrared thermometers see through water?

No. Infrared thermometers can only measure the surface temperature of water.


What is spot size, spot ratio, or distance-to-target ratio?

The “spot size” of any given measurement is controlled by two variables:

  1. The distance-to-target ratio (or spot ratio) of your particular infrared thermometer
  2. The distance between your infrared thermometer and the target

Typically listed on the thermometer itself, the distance-to-target ratio (DTR)  –  or spot ratio – tells you the diameter of the circle of surface area an IR thermometer will measure at a given distance.

For example, an infrared thermometer with a 12:1 DTR ratio will measure the temperature of a 1-inch diameter circle of a surface area from 12 inches away.


Do I need to clean my infrared thermometer?

To be accurate, infrared thermometers must be kept free of dirt, dust, moisture, fog, smoke, and debris. Always take the time to clean your infrared thermometer after exposure to dirty, dusty, smokey, or humid conditions. You should also plan a regular cleaning every six months or so. Particular care should be taken to keep the infrared lens and tunnel clean and free of debris.

To clean your infrared thermometer:

  • Dip a soft cloth or cotton swab in medical alcohol (never use soap or chemicals).
  • Carefully wipe the lens first and then the body of the thermometer.
  • Allow the lens to dry fully before using the thermometer.
  • Never submerge any part of the thermometer in water.


How do I turn the laser on?

It depends upon the particular model of infrared thermometer. Consult the user’s manual that came with your thermometer for the full range of features and how to use them.


Why am I getting weird readings on shiny metal?

Substances with very low emissivity ratings, like highly-polished metals, tend to be very reflective of ambient infrared energy and less effective at emitting their own electromagnetic waves. For example, if you were to point an infrared thermometer with fixed emissivity at a stainless steel pot, the reading will be incorrect because shiny metal is better at reflecting the ambient radiation of the room than it is at emitting its own infrared radiation.

Some infrared thermometers have fixed emissivity settings (usually of 0.95 or 0.97) to simplify their operation while leaving them suitable for most organic materials, including almost all foods. Other infrared thermometers come with adjustable emissivity settings, so you can more accurately prepare your thermometer for the type of surface being measured, particularly when measuring non-organic materials.


Can I calibrate my infrared thermometer myself?

Infrared thermometers can be calibrated for accuracy just like other thermometers. In calibration labs (like the ThermoWorks’ Calibration Laboratory (accredited by A2LA (American Association for Laboratory Accreditation), technicians use industrial black bodies (like the IR-500 Portable IR Calibrator) to calibrate infrared thermometers.

If neither an industrial black body or a comparator cup are available, you can do a quick calibration using a properly made ice bath.


Need More Help?

To arrange for an accredited calibration certificate, contact our Calibration Lab team by calling 1-800-393-6434 or by emailing

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