What size men's underwear do I need? How to measure the right size

A size S from one underwear brand does not necessarily fit the same as a size S from another. Your usual clothing size is therefore not always the best starting point when buying men's underwear. The most reliable way to determine your size is to measure your waist and compare that measurement with the brand's size chart.

In this blog, you can read how to do that, why sizes can differ between brands and what to consider for briefs, boxer trunks, jockstraps and men's thongs.

How do you determine the right men's underwear size?

Short answer: measure your waist circumference where the waistband of your underwear sits and compare the number of centimetres with the brand's size chart. Do not automatically choose the same S, M, L or XL you wear with another brand.

Underwear brands generally link their sizes to a waist measurement in centimetres or inches. Those size ranges are not universal: different brands can recommend a different size for the same waist measurement.

You can see the same difference in general size charts. Major clothing brands and retailers do not all use exactly the same centimetre ranges for S, M and L. A brand-specific size chart is therefore more important than a general conversion.

How to measure your waist for men's underwear

1. Preferably use a flexible measuring tape. If you do not have one, use a tape measure together with a piece of string or cord.
2. Measure directly against the skin or over very thin clothing.
3. Stand upright in a relaxed position and do not pull your stomach in.
4. Place the measuring tape horizontally around your body, exactly where the waistband of the underwear would sit.
5. Do not pull the tape tightly: it should sit against your body without pressing into the skin.
6. Write down the measurement in centimetres and compare it with the size chart for the product or the relevant brand.

No flexible measuring tape at home? Place a piece of string or cord around your body where the underwear waistband would sit, mark where the ends meet and then measure that length with a tape measure.

The exact measuring instructions can vary slightly by brand. Some size charts refer to the natural waist, while others refer to the position where the underwear is worn. Always follow the brand's measuring method when one is available.

Why isn't my underwear size the same with every brand?

There is no universal S, M or L for men's underwear. Brands decide for themselves which waist measurement corresponds to each size. The style, fabric and amount of stretch also affect how a product feels.

This means you may wear M with one brand and L with another, for example. That does not automatically mean a brand 'runs small'. Look first at the stated centimetres. International size labels can differ as well.

How does the material affect size and fit?

The size chart remains the starting point, but the material determines how much flexibility you have within a size. Underwear made from a thin and highly elastic fabric can adapt to your body more easily. The same size is therefore less likely to feel too restrictive than with a thicker, firmer or less stretchy material.

Do not look only at the main fabric. The elasticity of the waistband, leg openings and pouch also affects how close a style feels. Two styles with the same size and a similar waist measurement can therefore still feel very different.

Between two sizes? With a flexible, highly elastic style, you often have a little more margin. With a firmer fabric that has little stretch, the larger size may be more worth considering if you prefer your underwear not to feel too close. Always follow the brand's sizing advice first.

Should you use your trouser size for underwear?

Your trouser size can provide a first indication, but it is not the best measurement. Trousers are worn at different heights and the size on the label does not always correspond directly with your actual waist measurement. Measuring in centimetres therefore gives you a more useful starting point.

Once you have measured your waist, keep the measurement. It makes comparing different underwear brands much easier.

Which size should you choose if you are between two sizes?

If you fall exactly between two sizes, first look at the brand's advice and then at the material. A thin, highly elastic fabric generally gives more freedom of movement than a thicker, firmer or less stretchy material. If you prefer underwear not to feel too close, the larger size is more likely to make sense with a firmer style.

Do not automatically choose a smaller size because you think sexy men's underwear should fit as closely as possible. The wrong size can cause a waistband to roll, seams to pull or the style to sit differently from how it was designed.

Do you need a different size for a jockstrap?

With a jockstrap, waist measurement is also usually the most important starting point. The open rear does not automatically change your size. The elastic straps around the buttocks and the shape of the pouch can, however, feel different depending on the brand and style.

For a jockstrap, use the size chart of the specific brand rather than automatically ordering the same size you wear with another brand.

What size men's thong do you need?

The same principle applies to a men's thong: measure your waist and follow the size chart. The amount of fabric at the back says nothing about the size of the waistband. Differences in pouch, rise and stretch can still make two thongs in the same letter size feel different.

And for a brief or boxer trunk?

With a brief and boxer trunk, the waist is again the main starting point. With a boxer trunk, the leg openings and the stretch of the fabric also affect the wearing experience. If you have larger thighs, look not only at the waistband but also at the product description and material.

Centimetres matter more than S, M or L

The most important rule when choosing men's underwear is simple: compare your measured waist circumference with the size chart of the brand you want to buy. A general chart can be useful as an indication, but it should not replace a brand-specific size chart.

This prevents you from choosing a size based only on what you wear with another brand and makes it easier to compare brands with different sizing systems. If you want to compare different styles side by side, you can find them in the men's underwear overview.

Frequently asked questions about men's underwear sizes

How do I know what size underwear I need?

Measure your waist where the underwear waistband would sit and compare the number of centimetres with the brand's size chart. If you do not have a flexible measuring tape, you can use string or cord and then measure that length with a tape measure. Do not rely only on the size you wear with another brand.

Where should I measure my waist for underwear?

Measure horizontally around your body where the underwear waistband would sit. Use the brand's specific measuring instructions when available.

Is size M the same with every underwear brand?

No. The centimetre ranges for S, M, L and other sizes can vary by brand. Always check the size chart again when trying a new brand.

Should I size up for a jockstrap or thong?

Not automatically. Use your waist measurement and the brand's size chart. The style may feel different, but that does not automatically mean you need another size.

What should I do if my waist falls between two sizes?

Follow the brand's advice first. Then look at the material and amount of stretch. A thin, highly elastic fabric often gives a little more flexibility than a firmer material with limited stretch. When in doubt, the product- or brand-specific size chart is the deciding factor.

Dave from GUNDERWEAR

Last updated: 18 August 2026