1. Fill Container with Ice
Start by filling a tall cup or container with ice. ThermoWorks, the maker of our favorite digital thermometer, recommends using crushed ice since it results in less space between pieces of ice than whole cubes would. Make sure to fill the container to the top.
2. Add Water
Slowly add water to the container until all but the top ½ inch of ice is covered with water. Allow it to sit for a couple of minutes. If the ice at the bottom of the container starts to float, you need to add more ice and water.
3. Take the Temperature
Place the thermometer probe into the ice-water mixture. You want to take care to stir it in the center of the container, avoiding the walls of the container. The thermometer should read 32°F in the ice bath, plus or minus the manufacturer’s specified accuracy. If your thermometer can be calibrated, you can adjust it so that it measures 32°F in the ice bath.
Information adapted from thermoworks.com.