How to Choose the Right Size in Boxer Shorts and Trunks

Quick Answer

To choose the right size in boxer shorts and trunks, measure your waist at the narrowest point and compare it to the brand's size chart. If between sizes, consider the rise and your preferred fit: for a classic fit, size up; for a snug, supportive fit, size down. Always check the fabric composition, as stretch affects how the garment conforms to your body.

Finding the right size in boxer shorts and trunks is more than just picking a number on the waistband. A well-fitted pair supports without digging, moves with you without riding up, and feels almost invisible. This guide walks you through measuring your waist, understanding fit preferences, and applying simple decision rules to any brand's size chart.

Whether you're shopping for yourself or as a gift, knowing how to measure and what to look for in a size guide will save you returns and ensure comfort. Below, we cover the key steps, the trade-offs between snug and relaxed fits, and how materials like cotton and modal influence sizing.

How to Measure Your Waist for Underwear

Start with a soft measuring tape. Wrap it around your waist at the narrowest point, usually just above the belly button. Keep the tape snug but not tight, and make sure it's level all the way around. Breathe normally and take the measurement after exhaling to get a consistent number.

If you're between sizes, don't automatically round up or down. Look at the size chart's rise and hip measurements. For a low-rise trunk, the waistband sits lower, so your hip measurement may be more relevant. For a classic boxer short with a higher rise, the waist measurement is the primary guide.

• Measure at the natural waist, not where you wear your trousers.
• If you're between sizes, consider the fabric's stretch: cotton with spandex offers more give than 100% cotton.

Understanding Fit: Snug vs. Relaxed

Boxer shorts and trunks come in different fits, and personal preference plays a big role. A snug fit offers support and stays in place during active days, while a relaxed fit provides more breathability and freedom. The right choice depends on your daily activities and comfort priorities.

Consider the rise as well. A shorter rise creates a more modern, athletic look, while a longer rise offers more coverage and prevents riding up. If you're between sizes, a longer rise often accommodates a larger waist more comfortably, while a shorter rise may feel tighter.

• For active days or sports, choose a snug fit with stretch fabric.
• For lounging or sleep, a relaxed fit in soft cotton is often more comfortable.

Fabric and Stretch: How They Affect Sizing

The material composition influences how a garment stretches and conforms. Pure cotton offers minimal stretch, so it may shrink slightly after washing and requires a more precise size. Fabrics with elastane or modal provide more give, allowing a smaller size to fit comfortably without feeling restrictive.

For example, a trunk made from a cotton-elastane blend will hug your body more closely, so you might choose your true size or even size down for a supportive fit. On the other hand, a 100% cotton boxer short with a relaxed silhouette may feel better one size up if you prefer a looser feel.

• Check the fabric content in the product description: look for elastane or spandex for stretch.
• If you prefer a loose fit, consider sizing up in pure cotton styles.

Decision Rules for Choosing Your Size

• Measure first, always: Use a soft tape to measure your waist at the narrowest point. Compare to the brand's size chart, not your trousers size. Your number on the chart is your starting point.
• Check the fabric stretch: Look for elastane or modal blends if you want a snug fit with movement. Pure cotton styles have less give, so consider sizing up if you prefer a relaxed fit. Stretch changes the fit: more stretch means a smaller size can work.
• Consider rise and coverage: A longer rise provides more coverage and may fit a larger waist more comfortably. A shorter rise suits athletic builds and modern styling. Rise affects how the waistband sits and how the garment feels.
• When between sizes: For a classic boxer short, size up for a relaxed fit. For a trunk or brief, size down for a supportive fit, provided the fabric has stretch. Choose based on your preferred fit, not just the number.

ZIMMERLI Sizing and Fit Examples

• ZIMMERLI & HIGHSNOBIETY | Collab Boxershorts, Unisex - weiss: These boxer shorts are made from 100% cotton and feature a relaxed silhouette with a buttoned fly. Because they are 100% cotton with a relaxed silhouette, they have limited stretch. If you are between sizes, sizing up may offer a more comfortable, breathable fit, especially if you prefer a looser feel.
• Sea Island | Boxer Brief / Trunk - blue horizon: This trunk is made from exclusive Sea Island cotton, handpicked in Barbados and knitted in Switzerland, known for its silky touch and luxurious feel. Sea Island cotton is exceptionally fine and soft, but like most pure cottons, it has minimal stretch. For a supportive fit, choose your exact waist size; if you prefer a bit more room, consider sizing up.

Which Fit Should You Choose?

Best for

• Snug fit trunks with stretch are best for active days and sports, offering support and staying in place.
• Relaxed fit boxer shorts in pure cotton are best for lounging and sleep, providing breathability and freedom.

Not for

• Snug trunks are not for those who prefer loose, airy underwear for everyday leisure.
• Relaxed boxer shorts are not for high-intensity workouts where support is crucial.

Choosing the right size in boxer shorts and trunks comes down to measuring accurately, understanding the fabric's stretch, and knowing your fit preference. Use the size chart as your base, apply the decision rules above, and you'll find underwear that feels made for you. When in doubt, consider the rise and the material to make the final call.