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Guide

How to Choose an Infrared Thermometer

Infrared thermometers are cheap, fast and easy to misuse. The specification that matters most is how big the measured spot is at the distance you work, followed by emissivity control, then range and accuracy. Here is how to pick one for kitchens, HVAC, electrical checks and building surveys.

By the Akermin Editorial Team · 3 min read

As an Amazon Associate, Akermin earns from qualifying purchases. Product links on this page are affiliate links.

Choose an infrared thermometer by first working out the smallest target you need to read and from how far: the distance-to-spot ratio (12:1, 30:1, 50:1) must give a spot smaller than the target at that distance. Then require adjustable emissivity unless every target is matte and non-metallic, a temperature range that covers the hottest job (cooking surfaces and exhaust manifolds need 500 °C or more), a stated accuracy of ±1 to 2 °C, and a laser that shows the spot boundary (dual or circle laser) rather than just its center. Add a K-type probe input for contact readings and data hold or logging if the readings go into a record.

Step 1: Spot size

The thermometer averages the temperature over a circle whose diameter grows with distance. Spot = distance ÷ D:S ratio.

D:S ratio Spot at 30 cm Spot at 1 m Spot at 3 m
8:1 38 mm 125 mm 375 mm
12:1 25 mm 83 mm 250 mm
30:1 10 mm 33 mm 100 mm
50:1 6 mm 20 mm 60 mm

The target should be at least twice the spot size for a clean reading. A 12:1 unit reading a 20 mm terminal must be within 12 cm; a 30:1 unit can be 30 cm away.

Step 2: Emissivity

Fixed-emissivity units assume 0.95, which is right for food, painted surfaces, wood, drywall and skin and wrong for stainless, aluminum, copper, glass and galvanized steel. Adjustable emissivity, or at least a few presets, makes the thermometer usable on metal with the tape-patch method. See how to set emissivity; the physics is identical.

Step 3: Range and accuracy

Use Range needed Accuracy
Kitchen (pans, oil, griddles, pizza ovens) −20 to 500 °C or more ±2 °C
HVAC (registers, coils, lines) −30 to 300 °C ±1 to 2 °C
Automotive (brakes, exhaust, radiators) −30 to 600 °C ±2 °C
Electrical (breakers, motors) −30 to 400 °C ±1 °C
Building surveys (surface temps, dew point checks) −30 to 100 °C ±1 °C

Step 4: Features

  • Laser: single-dot marks the center only; dual or circle lasers show the spot boundary and prevent aiming errors.
  • Response time: under a second for handheld use.
  • K-type input: lets the same meter take contact readings for calibration checks and for air temperature.
  • Max/min, hold, alarms: useful for scanning across a surface.
  • Logging and Bluetooth: for reports.
  • Thermal imaging hybrids: spot thermometers with a small thermal array (FLIR TG165-X class) show where the hot spot is before reading it. See thermal camera vs infrared thermometer.

Step 5: Using it correctly

  1. Know the spot size at your distance; get closer for small targets.
  2. Set emissivity for the surface, or read a tape patch on metal.
  3. Aim square-on; glancing angles read low.
  4. Let the thermometer equilibrate to the room; a cold unit reads low for minutes.
  5. Keep the lens clean; grease and dust scatter the reading.
  6. Remember it reads surface, not air, and not internal temperature of food.

Picks by use

  • Kitchen and general: a 12:1 unit with adjustable emissivity and a range to 550 °C (Etekcity 774 class).
  • Trade (HVAC, electrical): 12:1 or better with dual laser, adjustable emissivity and a K-type input (Klein IR1 and higher models).
  • Small distant targets: 30:1 or 50:1 professional units.
  • Finding rather than reading: a spot thermal camera.

Infrared thermometers and spot cameras are in the thermal and inspection category; for the camera route see best thermal cameras for home inspection.

Klein Tools IR1 Infrared Thermometer with Targeting Laser, Auto-Hold, More

Klein Tools IR1 Infrared Thermometer with Targeting Laser, Auto-Hold, More

View on Amazon
Etekcity Infrared Thermometer Laser Temperature Gun 774

Etekcity Infrared Thermometer Laser Temperature Gun 774

View on Amazon
Flir TG165-X Thermal Imaging Camera with Bullseye Laser, Spot IR

Flir TG165-X Thermal Imaging Camera with Bullseye Laser, Spot IR

View on Amazon

Products shown because their documented specifications fit this guide. Price and availability are on Amazon and can change.

Frequently Asked Questions

What does 12:1 mean on an infrared thermometer?

The distance-to-spot ratio: at 12 units of distance the measured spot is 1 unit across. At 60 cm the spot is 5 cm. Small targets need a higher ratio or a closer reading.

Do I need adjustable emissivity?

For anything other than matte, non-metallic surfaces, yes. Fixed 0.95 units misread stainless pans, bare metal, glass and aluminum ducts by tens of degrees.

Can an infrared thermometer measure air temperature?

No. It reads surfaces only. For air, use a probe thermometer or thermohygrometer.

Affiliate disclosure: Akermin earns a commission from qualifying Amazon purchases made through links on this page. Our editorial picks are based on documented specifications and owner feedback, not commissions.