How Do Swim Trunks Fit by Inch? The Ultimate Guide to 15", 17", 18", 19", 20", 21" and 22" (2026)

When you're looking for surf swimwear from brands like Billabong, Rip Curl, Quiksilver, or Vissla, it's very common to find numbers like 17", 19", or 21" in the description. Many people think they refer to the size, but in reality, they indicate the length of the swim trunks.

Choosing the right length is almost as important as choosing the correct size. The same pair of swim trunks can exist in size M with a 17-inch or 21-inch cut, offering a completely different style.

In this guide, we explain what the inches on swim trunks mean, how each length fits, and why knee-length swim trunks have made a strong comeback in 2026.

What do the inches on swim trunks mean?

The inches indicate the outer length of the swim trunks, measured approximately from the top of the waistband to the end of the leg.

They do not refer to the waist or size.

For example, swim trunks can be:

• Size M and 17"

• Size M and 19"

• Size M and 21"

The size determines the waist circumference, while the inches indicate the length of the swim trunks.

For reference:

• 1 inch = 2.54 cm

Approximate inch equivalent

Measurements may vary slightly between manufacturers but serve as a general reference.