You’re standing in the baking aisle. One hand grips a bag of icing sugar, the other reaches for powdered sugar. Your recipe calls for one, but the store only seems to have the other, or maybe they have both and the price difference is just weird enough to make you pause. Honestly, it’s one of those kitchen dilemmas that feels like it should be a big deal, but half the time, it’s just marketing. Or is it?
Most people think they’re identical. They aren't. Well, they usually are, but it depends entirely on where you live and what you’re trying to whip up for dessert tonight. If you're in the United States, you're basically looking at the same thing with two different names on the box. But head over to the UK, Canada, or Australia, and the terminology starts to shift, sometimes referring to the fineness of the grind or the specific anti-caking agent tucked inside that white cloud of dust.
It’s confusing. I get it.
The difference between icing sugar and powdered sugar often comes down to a tiny percentage of cornstarch and how many times the sugar crystals were pulverized in a giant industrial mill. If you mess this up in a delicate macaron or a stiff royal icing, you’re going to know it. Your frosting might end up gritty, or worse, it could turn into a puddle because the starch content wasn't there to stabilize the structure.
The Chemistry of the Crunch
Let’s talk about what’s actually inside the bag. Regular granulated sugar is sucrose. When you take those hard little crystals and smash them into a fine dust, you get what we call "10X" sugar in the industry. That "10X" refers to the number of times the sugar has been processed through the milling machine.
But there’s a problem.
Sugar is hygroscopic. That’s a fancy way of saying it loves water. It sucks moisture out of the air like a sponge. If you just ground up pure sugar and put it in a box, it would turn into a literal brick within forty-eight hours. To stop this from happening, manufacturers add a flow agent. Usually, this is cornstarch, but sometimes you’ll see potato starch or even calcium phosphate in higher-end or organic brands.
This is where the nuance of the difference between icing sugar and powdered sugar starts to appear. In many regions, "icing sugar" is the catch-all term for this sugar-plus-starch mixture. However, professional bakers sometimes distinguish between "confectioners' sugar" (which always has starch) and "snow sugar" (which is coated in fat to prevent melting on hot donuts).
Why the Starch Matters More Than You Think
Have you ever tried to make a simple syrup using powdered sugar? It’s a disaster. The cornstarch makes the liquid cloudy and gives it a weird, chalky aftertaste. This is the first rule of the kitchen: never use powdered sugar when the recipe calls for granulated, even if you think the "fine texture" will help it dissolve faster. It won’t. It’ll just make your cocktail or sauce taste like a basement.
On the flip side, that starch is your best friend when making buttercream. It provides a structural backbone. Without that 3% to 5% of cornstarch, your frosting would lack the "crust" that many American-style buttercreams are known for.
Regional Names and Labeling Chaos
If you’re reading a British cookbook, like something from Mary Berry or Nadiya Hussain, they’ll almost always say icing sugar. In the US, C&H or Domino labels might say "Powdered Sugar" in huge letters and "Confectioners" in tiny print underneath. They are, for all intents and purposes, the same product.
But wait.
There is a third player: pure icing sugar. This is a niche product found more commonly in Australia and the UK. It contains zero starch. It is 100% pulverized sugar. If you use this in place of regular powdered sugar in a standard frosting recipe, your icing will be significantly softer and more prone to weeping. Pure icing sugar is specifically for royal icing—the kind that gets rock hard on gingerbread houses—where you want absolute purity and no interference from starches.
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The 10X Factor
In commercial kitchens, you might hear chefs talk about 6X or 10X sugar.
- 6X sugar is slightly coarser. It’s great for dusting on top of a cake because it doesn't melt quite as fast.
- 10X sugar is the standard "powdered" variety you find at the grocery store. It’s ultra-fine.
If you’re at a specialty bakery supply store and see 12X, grab it. It’s like silk. It makes the smoothest fondant you’ve ever tasted. But for the average person making cupcakes on a Sunday, 10X (powdered sugar) is the gold standard.
Can You Make It at Home?
Yes. Sort of.
If you run out of icing sugar in the middle of a bake, don’t panic. You can throw regular white granulated sugar into a high-speed blender (think Vitamix or Ninja) and whiz it until it looks like smoke.
Here is the kicker: you must add cornstarch if you plan on storing it.
Pro-tip: The ratio is generally one tablespoon of cornstarch for every cup of granulated sugar.
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But fair warning—home-ground sugar is rarely as fine as the industrial stuff. If you use a standard food processor instead of a high-powered blender, your "powdered" sugar will actually be "caster" sugar—a middle-ground texture that’s great for meringues but will make your frosting feel like it’s full of sand.
When the Difference Actually Ruins a Recipe
Let's get into the weeds of the difference between icing sugar and powdered sugar when it comes to high-stakes baking.
Take French Macarons. These temperamental little cookies rely on a very specific ratio of almond flour to sugar. Most professional pastry chefs, like Pierre Hermé, insist on a powdered sugar that has a specific type of starch. If you use a "pure" icing sugar without starch, the shells will often crack because there’s nothing to absorb the excess moisture from the egg whites during the "resting" phase.
Then there’s the "Snow Sugar" (also known as non-melting sugar). This is a different beast entirely. It’s often labeled as powdered sugar in professional catalogs, but it’s treated with carnauba wax or other fats. If you see a beautiful lemon tart in a bakery window and the white sugar on top isn't dissolving into the wet curd, that’s not regular icing sugar. It’s snow sugar. If you try to swap regular powdered sugar for that, it will disappear into the tart in about five minutes.
Sifting: The Step Everyone Skips
Regardless of what the label says, both icing and powdered sugar share one annoying trait: lumps.
Because of that moisture-loving nature we talked about earlier, these sugars form tiny pebbles in the bag. If you dump them straight into your butter, those pebbles will stay there. You’ll end up with a "polka dot" frosting where you get a literal hit of raw sugar dust when you bite in.
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Always sift. Always. It doesn't matter if the bag says "pre-sifted." It’s lying. The weight of the bags being stacked on top of each other at the grocery store compresses the sugar into lumps anyway.
Summary of Usage
- American Buttercream: Use standard powdered sugar (10X). The cornstarch helps it crust.
- Royal Icing: Use pure icing sugar if you can find it for a harder set, otherwise standard powdered is fine.
- Meringues: Use caster sugar (superfine), not powdered. The starch in powdered sugar can mess with the protein bonds in the egg whites.
- Dusting Brownies: Use powdered sugar, but wait until they are completely cool, or use "Snow Sugar" if you want it to last overnight.
How to Store It So It Doesn't Turn Into a Rock
The difference between icing sugar and powdered sugar doesn't change the storage requirements. Both hate humidity. If you live in a swampy climate, the paper bag it comes in is your enemy.
Transfer the sugar to an airtight plastic or glass container immediately. Some people swear by putting a terracotta "sugar saver" in there, but that’s actually for brown sugar to keep it moist. For powdered sugar, you want the opposite. Throwing a small silica gel packet (the food-safe ones) in the container can keep your sugar flowing like silk for a year or more.
Actionable Steps for Your Next Bake
Don't let the semantics trip you up. If a recipe is from a US-based site, buy "Powdered Sugar." If it’s from an international site, buy "Icing Sugar."
- Check the ingredients list on the back of the bag. If it says "Sugar, Cornstarch," you have the standard product used in 95% of recipes.
- Feel the bag. If it feels like it has hard rocks inside, you'll need to use a fine-mesh sieve. No excuses.
- Taste a pinch. If it feels gritty on your tongue, it's a lower-quality grind (likely 6X). Use this for cookies, but maybe not for a smooth Swiss Meringue Buttercream.
- Measure by weight. A "cup" of powdered sugar can vary by 20 grams depending on how packed it is. Use a digital scale to hit the exact grams called for in the recipe to avoid a dry, stiff mess.
You now know more about the difference between icing sugar and powdered sugar than most people ever will. It's usually the same thing, just wearing a different hat depending on where you're shopping. Use the 10X variety with cornstarch for your frostings, keep it bone-dry, and always, always sift it before it hits the mixing bowl.