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Point the gun at the surface, not into a gap or at a shiny cover, and hold it at a distance where the spot is smaller than the feature you care about. Set emissivity to match the surface if the instrument allows it. Read the number as the average temperature of everything inside the spot, not as a point measurement. For most household and trade checks the method matters more than the instrument, which is why a basic 12:1 gun such as the Etekcity Lasergrip 774 can give a sensible answer on a matt surface while a premium gun gives a wrong one on polished metal.
What the spot is, and why your distance changes the answer
Every infrared thermometer has a distance-to-spot ratio, usually written as something like 12:1 or 16:1. The first number is the distance from the lens, the second is the diameter of the area the instrument averages, in the same units. A 12:1 gun held 36 cm from a wall is reading a circle roughly 3 cm across. That is the arithmetic the listing for the Etekcity Lasergrip 774 is pointing at when it recommends 36 cm for best results: at that distance the spot is a manageable size and the reading is close to the target.
The mistake is to treat the laser dot as the measurement point. On a single-laser gun the dot shows roughly where the centre of the spot is, not its size. On a two-laser gun such as the TempPro TempScan the two dots converge at the stated ratio, so at the correct distance they bracket the spot. Move closer and the dots separate; move further and they cross. Either way the spot is still a circle with area, and the instrument reports the average of everything in it.
This matters when the target is small or when there is a hot or cold background behind it. Reading a 5 mm pipe from a metre away with a 12:1 gun means the spot is about 83 mm across, so most of what you are measuring is the air and the wall behind the pipe. The same arithmetic applies to a single warm terminal in a cool enclosure. Get close enough that the spot fits inside the feature, or accept that the number is a blend.
Emissivity: the setting that decides whether the number is real
Infrared thermometers do not measure temperature directly. They measure the infrared energy leaving a surface and convert it using an assumed emissivity, a number between 0 and 1 describing how efficiently that surface radiates compared with a perfect black body. Most guns are fixed at around 0.95, which is close to matt paint, cardboard, food, brick and most oxidised metals. On those surfaces the default is fine.
On shiny metal the default is wrong. Bare aluminium, polished stainless steel and copper have low emissivity, often below 0.2, so they radiate little of their own energy and reflect the surroundings instead. A gun set to 0.95 will read a low or erratic number that tracks whatever is behind you rather than the metal. Adjustable emissivity, as offered on the Etekcity dual laser model and the TempPro TempScan, lets you set a value closer to the surface you are measuring. The listing does not publish a table of values, and neither does most packaging; the practical fix for a shiny surface is a piece of matt tape or a dab of flat black paint, allowed to reach the same temperature as the metal, then measured with the default setting.
Reflection is the other half of the problem. A shiny surface acts partly as a mirror, so a gun pointed at a stainless flue may be reading the temperature of the room reflected in it. Changing your angle changes the reading. That is the signature of a reflection error, and no emissivity setting fully removes it; you have to change what you are pointing at.
Aiming and holding: the routine that gives repeatable readings
The trigger on most guns is a continuous measurement button. Hold it down and the display updates; release it and many models hold the last reading for a few seconds. That hold is useful for reading a number in an awkward position, but it also means a stale value can look like a live one. The listing for the dual laser Etekcity mentions automatic data hold and a maximum hold, which records the highest value seen during a sweep. Maximum hold is how you find the hot end of a radiator or the peak of a cycling compressor, but only if you sweep slowly enough for the instrument to see it.
Response time is stated as less than half a second on the Lasergrip 774 and 0.5 s on the TempScan. That is the time to settle after the target enters the spot, not a guarantee that the surface itself has reached a steady temperature. On a heating duct or an engine block, wait for the reading to stop moving before you write it down.
Ambient temperature affects the instrument as well as the target. A gun that has been in a cold van or a hot cab needs time to settle before its readings are meaningful. The listings here do not publish an operating ambient range, so the honest guidance is to let the instrument sit in the environment for a while rather than trusting the first number after a move.
Reading the table: what the specifications actually tell you
The four instruments referenced in this guide differ in range, ratio and adjustment, and the table below lines up the figures the listings publish. Where a listing is silent, the cell says so rather than guessing.
| Instrument | Stated range | Distance-to-spot | Emissivity adjustment | Response |
|---|---|---|---|---|
| Etekcity Lasergrip 774 | -50 to 450 C | 12:1 | Not stated in the listing bullets | Under 0.5 s |
| Etekcity dual laser | -50 to 550 C | 12:1 | 0.1 to 1.0 | Not stated in the listing bullets |
| Fluke 62 Max+ | 22 to 1202 F | Not stated in the listing bullets | Not stated in the listing bullets | Not stated in the listing bullets |
| TempPro TempScan | Not stated in the listing bullets | 16:1 | 0.1 to 1.0 | 0.5 s |
Two things stand out. First, the Fluke listing gives an accuracy figure, 1 C or 1 percent of reading between 0 and 650 C, and a dual laser that rotates to bracket the spot. That is the kind of specification a technician uses to decide whether a reading is inside tolerance. Second, the cheaper guns publish range and ratio but not accuracy, which is not the same as being inaccurate; it means the buyer has no stated figure to work from. If your work needs a tolerance, choose an instrument whose listing states one. If it needs a quick relative check, a 12:1 gun is enough.
The maximum range figure is the least useful number on the box for most buyers. A gun that reads to 550 C is not more accurate at 40 C than one that reads to 450 C; the ratio and the emissivity setting decide that. The guide to choosing an infrared thermometer covers the trade-offs in more depth.
Where the method stops working, and what to use instead
An infrared thermometer reads surface temperature. It does not read air temperature, core temperature or the temperature inside a wall. Pointing one at a window to judge the room, or at a person to check for fever, gives a number that is a surface reading of glass or skin and is not a substitute for the measurement you actually wanted. The listing for the dual laser Etekcity says plainly that it is not for human use, and that is true of the whole class.
Inside a wall, behind a panel or under insulation, the surface you can see is not the surface you care about. A thermal camera shows the pattern across a surface, which is often more useful than a single spot, but it still reads surfaces. The comparison between a thermal camera and an infrared thermometer is worth reading before you buy either for a diagnostic job.
Air temperature and humidity need a different instrument. A psychrometer measures the wet and dry bulb temperatures and derives relative humidity, which an infrared gun cannot do. If your question is about air rather than a surface, start with how to use a psychrometer.
Finally, a gun is not an alarm. It gives a reading when you point it and pull the trigger; it does not watch a process or warn you when something changes. For continuous monitoring you need a fixed sensor or a data logger, not a handheld.
The habit that makes the reading trustworthy
Before you trust the number, ask three questions: is the spot smaller than the feature, is the surface matt or shiny, and has the instrument settled. If the answer to any of them is no, change the setup rather than the instrument. The gun is the cheapest part of the measurement; the method is what you are actually buying.
Frequently Asked Questions
Can I use an infrared thermometer to check if my oven is at the right temperature?
You can read the surface temperature of the oven wall or a pizza stone, but not the air temperature inside, which is what the dial refers to. The reading will also depend on emissivity: a shiny oven interior reflects, so a matt stone or a piece of baking parchment gives a more reliable number. Use it to compare surfaces, not to calibrate the oven.
Why does my reading jump around when I point at metal?
Low-emissivity metal reflects its surroundings, so the gun is partly reading the room. Change your angle and the number changes, which is the giveaway. Put a piece of matt tape on the metal, let it settle, and measure the tape with the default emissivity setting.
Does the laser measure the temperature?
No. The laser is an aiming aid only. The measurement is the infrared energy collected by the lens, averaged over a spot whose size is set by the distance-to-spot ratio. A single dot shows roughly the centre of the spot; two dots that converge show its width at the stated distance.
How far away should I hold the gun?
Close enough that the spot fits inside the feature you are measuring. Divide the distance by the ratio to get the spot diameter: a 12:1 gun at 36 cm reads a spot about 3 cm across. The Etekcity listings recommend 36 cm for best results, which is a sensible working distance for a 12:1 instrument.
Can it measure body temperature?
No. The listings for these instruments state they are for inanimate objects, and skin surface temperature is not core temperature. A dedicated clinical thermometer is the right instrument for a person.
What does the maximum hold do?
It records the highest reading seen while the trigger is held, so you can sweep across a surface and then read the peak. It is useful for finding the hot end of a radiator or a cycling compressor, provided you sweep slowly enough for the instrument to see each point.