Last updated: 2026-07-13

Candy and Sugar Temperature Stages

Candy making is really sugar-concentration cooking. As a sugar syrup boils, water evaporates and the syrup grows more concentrated, and the more concentrated it becomes, the hotter it gets and the harder it sets when cooled. That relationship is so reliable that confectioners name the classic stages — thread, soft ball, firm ball, hard ball, soft crack, hard crack, and caramel — directly after the temperature the syrup has reached. This calculator turns a chosen stage into its target temperature and working range, and corrects both for your altitude.

The sugar stages

Each stage covers a narrow band of temperatures, and each band produces a characteristic texture once the syrup cools. Fudge and fondant are cooked to the soft-ball stage; caramels sit at firm ball; toffee and brittle go all the way to hard crack; and true caramel comes last, where the sugar itself begins to brown.

The single target the calculator shows for each stage sits inside its band — 114 °C for soft ball, 150 °C for hard crack, and so on — and is a safe reading to aim for. The range around it tells you how much room you have before the sugar tips into a softer or firmer set.

The cold-water test

Long before candy thermometers were common, cooks judged sugar by dropping a little hot syrup into a bowl of very cold water and feeling the result with their fingers. The test still works and is a good backup:

• Thread: the syrup spins a soft, thin thread as it falls.
• Soft ball: it gathers into a ball that flattens as soon as you lift it from the water.
• Firm ball: the ball holds its shape but still yields to pressure.
• Hard ball: the ball is firm and holds its shape, giving only a little.
• Soft crack: the syrup separates into firm but pliable threads.
• Hard crack: it forms brittle threads that snap cleanly.

Beyond hard crack the sugar stops behaving like a syrup and starts to caramelize, turning from pale gold to deep amber. There the colour and smell are the guide, because a thermometer alone will not warn you before it scorches.

Why altitude matters

Sugar syrup reaches each stage when it is hot enough to hold the right concentration of water — but water boils at a lower temperature as you climb. At altitude the syrup therefore hits each stage at a lower thermometer reading, and cooking to the sea-level number would overshoot and leave the candy too hard.

A widely used rule is to subtract about 0.5 °C for every 150 m of elevation, roughly 1 °F for every 500 feet:

$T_{\text{stage}} = T_{\text{sea level}} - \frac{\text{altitude (m)}}{300}$

In Denver, near 1,600 m, that is close to a 5 °C reduction — enough to matter for a tight stage like soft ball. The calculator applies this correction to both the target and the range as soon as you enter your altitude, so the readings shown are the ones to aim for where you are cooking.

Getting a reliable reading

Because the stages are only a few degrees apart, an accurate thermometer matters more than an expensive one. Calibrate it first: clip it into boiling water and check that it reads the local boiling point (100 °C at sea level, lower at altitude). If it is off, apply the same offset to your target. Keep the bulb in the syrup but off the bottom of the pan, watch for the reading to hold steady rather than climbing, and pull the pan from the heat a degree or two early, since a hot pan keeps cooking the syrup after the burner is off.