The New ThermoWorks Thermapen ONE Instant-Read Thermometer: Tested and Approved

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Thermapen ONE Instant-Read Thermometer Tout

The Spruce Eats / Rachel Knecht

Our reviewer was sent a sample of the ThermoWorks Thermapen ONE Instant-Read Thermometer to the test in her kitchen. Keep reading for our product review.

Tested & Approved

The ThermoWorks Thermapen ONE Instant-Read Thermometer is accurate, reliable, and a great upgrade from its predecessor, the Thermapen MK4.

Though I've cooked for years, I find the most stressful part of dinner is deciding when it’s fully cooked. I grew up in a household that relied on the color of the meat to let you know when a piece of meat was fully cooked; any pink and it was off to the microwave until none remained. As I began cooking for my family, I would check, be unsure, and then put many chicken thighs and pork tenderloins back into the oven, which meant late dinners, dry meat, and a wish for an easier way! When I learned that the only reliable way to measure doneness and to see if you've reached the FDA recommended minimum safe temperature is to use a thermometer, I knew I needed one.

That's how I finally came to own a Thermapen MK4 and I still use it almost daily. And it's not just for meat—instant-read thermometers are important for baking, too. Knowing the ideal internal temperature of baked bread, custards, and even brownies makes my bakes much more consistent. When ThermoWorks replaced the MK4 with the Thermapen ONE, I couldn’t wait to get my hands on it to see how they compare.

ThermoWorks Thermapen ONE

ThermoWorks Thermapen ONE


What We Like
  • 1 second read time

  • Increased accuracy

  • Upgraded back light

What We Don't Like
  • Model not listed on the front

  • Not as comfortable for lefty

#1 Features

I’ve used the MK4 for years, and I could (and will) go on about all the things I like about it. Thankfully, the Thermapen ONE includes all the same features that I’ve grown to love. The number orientation still matches the direction you’re holding it, which is very helpful as a lefty. It has a sturdy body with a long probe that easily folds in and out. It also comes with a calibration certificate, and is available in bright colors in the minimalist design. It still automatically turns off for those times that I leave it on the counter instead of wiping it down and putting it away. Lastly, both Thermapens can read temperatures from negative 50 to 572 degrees Fahrenheit.

Thermapen MK4 thermometer and ONE thermometer with probes out

The Spruce Eats / Rachel Knecht

#2 Design

The Thermapen ONE and the Thermapen MK4 look and feel almost identical. The main physical difference is that the AAA battery on the Thermapen ONE is on the back of the thermometer instead of at the bottom. If I was playing "spot the difference," I’d circle the rubber band that the older model has that is missing from the ONE and maybe the slightly smaller curve at the bottom of the newer model. Other than that, I’d say that they look and feel 98% identical. Even the branding for both is the same but I do wish the model was listed on the front. I also feel that both are more comfortable to hold in the right hand than left since that causes the curve to face out.

The Thermapen ONE includes all the aspects that I like about the MK4 and enhances them.

#3 The Differences

The Thermapen ONE includes all the aspects that I like about the MK4 and enhances them. The MK4 takes 2 to 3 seconds to read, whereas the ONE reads in 1 second, which makes a big difference, especially when testing multiple locations of a large turkey or roast. 

Another aspect of the Thermapen ONE (and I didn’t think this was possible) is it's even more accurate than the MK4. The ONE reads temperatures within 0.5 degree Fahrenheit as opposed to 0.7 degree Fahrenheit. I didn’t think this difference would matter but as I held the two Thermapens up side-by-side, there could be a 1 to 2 degree difference in the reading.

Thermapen ONE next to a plate with a cooked chicken thigh and carrots

The Spruce Eats / Rachel Knecht

One final note …

Lastly, ThermoWorks upgraded the backlight for the screen. My kitchen is not well-lit and when the winter sun goes down at 4pm, I’m often cooking in low light. The backlight is now brighter and can be turned on by covering the sensor, which is an added bonus. You’ll never be struggling to read the temperature while reaching into a dark oven, or while grilling on a late summer evening. That alone makes this worth it.

Price at time of publish: $99

The Verdict

The Thermapen ONE exceeds expectations and improves on the MK4.

The Thermapen ONE is worth buying if you don’t own the discontinued MK4 or it’s no longer working. The ONE has a quicker read time, improved backlight, and greater accuracy than the previous model. It’s a bit of a splurge, but worth it.

Product Name: Thermapen ONE 

Product Brand: ThermoWorks

Price: $99

Range: -58 to 572 degrees Fahrenheit

Response time: 1 second

Dimensions: 6.1 x 0.74 x 1.7 inches 

Power: AAA battery

Warranty: 5 years

Why Trust The Spruce Eats?

Rachel Knecht is a recipe developer and food writer in Seattle. She wouldn’t be the cook or baker she is today without a quality instant-read thermometer in her hand.

Article Sources
The Spruce Eats uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Nutrition, C. for F. S. and A. (2022). Safe food handling. FDA.