How To: Calibrate Your Candy Thermometer

CATEGORIES: How To..., Kate

During December, we’re going to be doing some extra posts to help you guys make it through the holiday season with your sanity in tact!

This is a really quick tip that will help you in all your candy-making endeavors (like Apple Cider Caramels and Peanut Brittle). When you’re making candy, being able to accurately measure the temperature is absolutely essential, but how do you know if your candy thermometer is accurate or not?

First, you need a pot, any size, of water.

Clip the thermometer onto the side of the pan, making sure the knob on the bottom of the thermometer (anyone have a more accurate term for me? It’s 1:43 in the afternoon and I’m still in my pajamas if that gives you any idea of where my brain is right now…) isn’t touching the bottom of the pan.

Now, bring the pan of water to a rolling boil over high heat. Let it boil for 10 minutes (make sure you’re using a big enough pan that you have enough water to last 10 minutes). The boiling point of water is different depending on where you live (thanks readers!) so check this calculator to find out.   So, say your thermometer says 202 degrees, and you know that the boiling point is 212. You’ll know that you need to add 10 degrees to whatever your thermometer says. On the flip side, if the thermometer reads at 222 degrees, you need to subtract 10 degrees from whatever the thermometer is reading.

To make sure you remember, you can either write “+ ____” or “-____” (whatever the difference is) directly onto the thermometer with a Sharpie or onto a piece of tape that you can wrap around the thermometer or its protective sheath.

And…just in case you get confused by things like this (because I do ALL the time!), here it is in a nutshell:

–If the temperature reads above 212 F (or whatever your boiling point is), you need to subtract 212 from the number your thermometer is displaying and then, when you’re making candy, subtract that number from the reading you get on the thermometer.
–If the temperature reads below 212 F (or whatever your boiling point is), you need to subtract that number from 212. When you’re making candy, add that number to the number you get from the thermometer reading.

–Be sure to record how much you need to add or subtract in a place that’s easy to remember.
–Re-calibrate your thermometer at least once a year, or just buy a new one!

Happy holiday candy-making!!


  1. Help! Why is your blog the only one that comes up super tiny on my computer. Am I the only one? I can't read it and I am missing my OBB updates!!

  2. Thanks for the tips ladies! We like y'all so much that sometimes we forget you don't all live in our neighborhoods 🙂 I edited the info to reflect different boiling temps at different altitudes and linked that calculator. Thanks!

  3. you can use this method no matter where you are to see how much to adjust any candy recipe. as long as the candy recipe was written for sea level and you aren't already adjusting it for high altitude, this is a great way to know how much temperature to subtract off. the hard water is negligible. thermometers are not perfect.

    in conclusion, i like this idea. 🙂

  4. I have 2 Taylor candy thermometers and they actually read differently. The old one reads 204 when water is boiling, the new one reads 206. I ended up putting a post-it note on my fridge with these readings so that I could keep it straight. So, with the old thermometer, I take 8 degrees off what the recipe says, and with the other one, I take of 6.

  5. The boiling point of water is 212 only if you're at sea-level. For instance, I live about 4465 ft above sea-level, so the boiling point of water here is lower… around 203. It is a good idea to calibrate your candy thermometer, you just need to know the actual boiling point of water for your altitude. This website will do the calculation for you:

  6. what a great tip! this is especially great for people at high altitude (like me). i have attempted lots of candy recipes up here and had to try multiple times to get the temp right. this just makes so much sense…thank you!

  7. Um, sorry, but if you're not cooking at sea level, you'd better not do this. Water boils at progressively lower temperatures the higher you go. (Basic physics principle: Less pressure = lower boiling point.) For example, in Denver (5200 feet above sea level), water boils at 202 degrees Fahrenheit, not 212 (that's 94.7 degrees Celsius). In Salt Lake City (4400 feet), water typically boils at 204 degrees.

    The barometric pressure of the atmosphere that day will change the boiling point of water, too. If there's a low pressure weather system moving through your area, water will boil at a lower temperature than it would if there was a high pressure weather system and the skies was clear. (This may be part of why Grandma's caramels came out sticky on stormy days–not only was it humid, but she didn't boil them hot enough to compensate for the pressure being lower that day.)

    Having hard water (water with salts and other naturally-occurring minerals dissolved in it) also changes the boiling (and freezing!) point of water. It's the same reason we use salt to melt the ice on the driveway: The dissolving minerals raise the freezing point of the ice, helping it melt at lower temperatures than it normally would. Depending on how hard your water is, it may boil a fraction of a degree or even several degrees hotter than normal. And there's no way to know the exact amount it's off by (or whether it's your thermometer that's off) without measuring & analyzing the mineral content of the water and calculating the mineral density for each trace element.

    In short, it's really not worth "calibrating" your home thermometers. If you're not sure about a thermometer's accuracy, just replace it. There's really no reason why an intact thermometer would lose its accuracy over time. The companies that manufacture thermometers have standard conditions they use to make sure their products measure correctly–and their calibrations will be a lot more accurate than anything we can calculate at home.

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