How To · Fashion · Menswear
The Fit Guide: How to Size Menswear Correctly
Sizing charts lie. Your body doesn't. We'll teach you the five measurements that actually matter, so you stop guessing and start buying pieces that fit like they were made for you.
5 min read · IrisMenswear sizing is deliberately confusing. A medium at one brand fits like a small at another. Vanity sizing inflates numbers. International conversions create chaos. But here's the truth: fit isn't about the tag—it's about five specific measurements on your actual body. Once you know these numbers, you can buy with confidence, whether you're shopping in-person or online.
This guide walks you through the measurements that matter, how to take them accurately, and what to do with the information. No fitting room required. No guesswork. Just clarity.
Shoulders can't be altered easily. Get them right first, and everything else falls into place.
What you'll need.
- 01Soft measuring tape
- 02Pen and paper or notes app
- 03A second person (for sleeve measurement)
- 04Shoes you plan to wear with the garment
Step one · 2 minutes
Measure your shoulders
This is the foundation. Ask someone to measure straight across your back from the outer edge of one shoulder bone to the outer edge of the other. Keep the tape measure level and snug but not tight. Write this number down. Shoulder width rarely changes, and it's nearly impossible to alter in tailoring, so this measurement should drive your jacket and shirt size more than anything else.
Stand naturally with arms at your sides. Don't shrug or roll your shoulders back.
Step two · 2 minutes
Measure your chest
Wrap the tape measure around the fullest part of your chest, keeping it parallel to the ground. Don't pull tight—leave room for one finger to slip underneath. This is your true chest measurement. Compare it to brand-specific sizing charts, but remember that fit also depends on how a garment is cut. A slim-fit shirt at 38 inches will feel different from a regular-fit shirt at the same measurement.
Breathe normally. Don't puff out your chest or suck it in.
Step three · 2 minutes
Measure your sleeve length
Bend your arm slightly at the elbow. Measure from the center back of your neck, across your shoulder, down your arm to your wrist bone. This gives you your full sleeve length. For dress shirts, you want the cuff to hit just at your wrist bone when your arms hang naturally. For casual shirts and sweaters, sleeve length is more forgiving, but knowing your true measurement prevents ordering sleeves that are too short or too long.
Have someone help with this measurement—it's hard to do accurately on yourself.
Step four · 2 minutes
Measure your inseam and waist
For inseam: wear the shoes you plan to wear with the pants. Measure from your inner thigh down to the top of your shoe. For trousers, you want a slight break—about a quarter inch of fabric touching the shoe. For jeans, the hem should just graze the top of your shoe. For waist: measure around your natural waist (where your pants actually sit), keeping the tape snug but not compressing your body. This is different from your true hip measurement and matters more for fit.
Inseam changes based on shoe heel height. A dress shoe and a sneaker require different lengths.
Step five · 1 minute
Create your personal fit profile
Write down your five key measurements: shoulders, chest, sleeve length, inseam, and waist. Keep this list in your phone or wallet. When you shop online, check the brand's size chart against these numbers, not the size label. Different brands cut differently—a 40-inch chest in one brand might be a 42 in another. Your measurements are universal. Use them as your reference point, and you'll stop buying pieces that don't fit.
Screenshot or photograph your measurements. Update them annually or if your body changes.
Step six · 1 minute
Know what to ignore
Ignore the size label. Ignore what you wore five years ago. Ignore what your friend wears. Brands lie about sizing. Your body doesn't. Once you have your measurements, you're shopping with facts, not guesses. Some pieces will still fit differently based on fabric, cut, and design—that's normal. But you'll know immediately if a garment is worth trying on or if you should move on.
If a brand's size chart doesn't match your measurements, size accordingly. Don't force yourself into a number.
How to know it works.
You've nailed your sizing when you can predict fit before trying something on, when you rarely need tailoring beyond a hem, and when you stop buying pieces that looked good in photos but don't work on your body. Proper sizing is invisible—the clothes just fit.
Questions at the mirror.
What if I'm between sizes?
Size up. It's easier to tailor a garment down than to let it out. If you're between a medium and large, order the large and have the sides taken in if needed. Shoulders can't be altered, so prioritize getting that right.
Do I need different measurements for different garment types?
Your core measurements stay the same, but fit expectations change. A dress shirt needs a closer fit through the chest than a casual button-up. A sweater can be looser than a t-shirt. Know your measurements, then adjust based on the garment's intended fit.
How often should I remeasure?
Once a year or if your body changes significantly. Most men's measurements stay stable, but weight gain or loss, fitness changes, or aging can shift things. Update your profile accordingly.
What about international sizing?
Ignore it. Always reference the brand's actual measurements in inches or centimeters, not the EU or UK size label. A European 50 doesn't mean anything without the chest and shoulder measurements behind it.