What Size Curling Iron for Big Curls? | Barrel Guide

For the full breakdown, see our best Curling Iron for Big Curls guide.

Big curls start at 1.25 inches—that’s where loose, flirty shapes begin. But if you want true volume and movement rather than defined ringlets, a wider barrel makes all the difference. Here is the straightforward breakdown of what each size actually delivers, so you can match the tool to the look you have in mind.

Curling Iron Barrel Sizes Explained

Barrel diameter directly controls curl tightness. Smaller barrels wrap hair tightly, producing springy, defined curls. Wider barrels let hair coil loosely, which creates soft volume and gentle waves. If your goal is big curls, anything under an inch will work against you—it will deliver the tighter, smaller result you are trying to avoid.

• 1 inch — classic, defined curls
• 1.25 inches — loose curls, soft waves, an old-Hollywood feel
• 1.5 inches — soft curls, beachy waves, added volume
• 1.75 inches — big, voluminous waves, a convincing blowout effect
• 2 inches — very loose curls or broad waves, a true blowout finish

What Size for Big Curls on Long Hair?

Long hair is the ideal match for larger barrels. Your hair’s weight pulls curls downward as they set, so a tighter wrap on long strands often falls out before it registers as a curl. Wider barrels give long hair the room it needs to form loose, bouncy shapes that actually hold. For long hair, sources consistently point to 1.5 to 2 inches for the biggest results.

If you have medium or shoulder-length hair, a 1.25-inch to 1.5-inch barrel tends to give the best balance of body and definition. Fine or thin hair also cooperates better with the smaller end of that range—very wide barrels on fine hair can produce a wave so loose it looks straight by the end of the day.

How Do I Measure a Curling Iron Barrel?

Barrel size is simply the diameter of the cylindrical section where you wrap your hair, measured straight across the widest point. The quickest way to know your barrel size is to check the label on the box. If that is gone, grab a flexible tape measure and measure while the iron is cool, off, and unplugged.

One caution: tapered wands narrow toward the tip, so a single measurement can mislead. For those, measure the thickest part of the barrel, since that is where the largest section of your curl forms. Metric sizes translate easily—a 25 mm barrel is about 1 inch, 32 mm is about 1.25 inches, and 38 mm is roughly 1.5 inches.

Big Curl Barrel Sizes at a Glance

Here is the quick reference for matching barrel size to the final look you want.

Two common mistakes undermine the big-curl look. Choosing a barrel too small is the most frequent one—it quietly produces the tighter curls you were trying to avoid. The second is ignoring your hair’s length and thickness; very large barrels shine on longer, thicker hair but can disappoint on shorter or finer strands. For a thorough breakdown of specific tools that perform well across different hair types, our tested roundup of the best curling iron for big curls compares their strengths side by side.

If a defined curl is the goal, stay at 1.25 to 1.5 inches. If you want dramatic, voluminous waves with minimal effort, a 1.75-inch or 2-inch barrel removes most of the guesswork—allowing you to sweep large sections around the barrel for loose, soft results. Whichever size you choose, always measure with the iron cool, off, and unplugged, and let each section cool completely before brushing for the longest-lasting shape.