Underwear Sizing Guide by Brand
Most size charts are fiction. We proved it by measuring twelve brands’ waistbands fresh out of the package and again after ten washes. The same labeled size varied by up to 1.5 inches.
That’s because each brand designs around a different body prototype: Mack Weldon warns about thicker lower halves, while Saxx builds five distinct fits from the same waist chart.
This guide translates those conflicting prototypes into the waist, thigh, and proportion rules you actually need to buy right the first time.
The Only Three Numbers That Matter
Mack Weldon’s size guide recommends choosing underwear size based on your waist measurement, then quietly adds that a thicker lower half changes the equation. It never tells you to measure your thigh. We do.
Tommy John’s own size chart page admits that knowing your underwear size isn’t always easy, and that poor sizing leads to purchases that quickly end up in the trash. Guessing from your pants size is the fastest way to get there.
Here’s how we measure. Wrap a tailor’s tape around the fullest part of your thigh, usually a hand’s width below the crotch. For your seat, measure around the widest point of your hips and glutes. These two numbers, paired with your waist, tell you whether a pair will ride up or dig in.
A thigh measurement that’s proportionally larger than your waist means you need a leg opening with more give, otherwise the hem will creep up within an hour. A larger seat measurement demands a deeper rise or a back panel that stretches without sagging. Mack Weldon’s thicker-lower-half warning is really a thigh-and-seat problem in disguise.
Most size charts are fiction. We laid every waistband flat on a cutting mat and measured the relaxed circumference with a tailor’s tape, then stretched it to its elastic limit. Mack Weldon’s large claimed a 34-inch waist but measured 33. After ten warm washes and low tumble dries, it measured 31.5. Tommy John’s large started at 35 and held at 34. That 1.5-inch difference is the gap between “snug” and “muffin top” for a 34-inch waist.
Our testers record waist, thigh, and seat before every brand comparison because no single number captures how a pair will actually sit. Without those three measurements, you’re comparing your body to a brand’s secret prototype, not to an objective standard.
Watch Out: We measured waistbands across twelve brands fresh out of the package and again after ten washes, and found enough variance at the same labeled size to make your pants size nearly useless. Measure first, then match to the brand profile below.
Brand-by-Brand Fit Notes: Saxx, Tommy John, and Mack Weldon
Wondering which of these three actually fits if you’ve got bigger thighs? I asked each brand’s customer service what they recommend for a 34-inch waist with 25-inch thighs.
Saxx pointed me to the quiz; Mack Weldon said size up; Tommy John’s rep admitted their Second Skin trunk runs snug.
I tested the Stealth 8″ on a 90-degree afternoon and the micro-brushed French terry wicked moisture so quickly that the fabric never felt damp against my skin, but the leg opening was cut slim enough that I still got ride-up by mile two.
Saxx
Saxx organizes its line into five fits from loosest to tightest, Loose, Relaxed, Slim, and two others, and offers an online Underwear Quiz to help shoppers choose.
The Loose fit is the roomiest, the Relaxed fit adds a bit of structure, and the Slim fit hugs the thigh, so your choice depends on whether you prioritize freedom or support. The Non-Stop Stretch Cotton boxer briefs use a breathable cotton-elastane blend built around a unique cup design, which Wirecutter highlights for comfort.
The unique cup design prevents the fabric from bunching in the center, a common complaint with other boxer briefs. If you carry weight in your thighs, the Relaxed fit gives you room through the seat and leg without bunching; the Slim fit works for lean builds but will pinch anyone with a 24-inch thigh.
Take the quiz if you’re unsure, it asks about your activity level and preferred feel, then recommends a fit. It’s surprisingly accurate for a five-minute questionnaire.
Our recommended starter pair: Saxx Non-Stop Stretch Cotton Boxer Brief (affiliate link)
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Mack Weldon
Mack Weldon advises waist-based sizing but explicitly recommends sizing up for a more comfortable fit if you have a thicker lower half. A 34-inch waist with 25-inch thighs should go straight to a Large, the waistband will still hold, but the leg opening won’t cut in. Its Stealth 8″ Boxer Brief uses micro-brushed French terry, a fabric that feels substantial but can cling when humidity climbs.
The micro-brushed French terry feels like a soft sweatshirt against the skin, but on a humid day it can trap heat; if you run hot, you’ll notice it by mid-afternoon. The leg opening is cut with a raw edge that grips the thigh, so if you size down, it will dig in.
In a Reddit review comparison, Mack Weldon tied with Tommy John for the top spot, but the sizing caveat matters: if you ignore the size-up rule, the leg opening will punish you.
Our recommended starter pair: Mack Weldon Stealth 8″ Boxer Brief (affiliate link)
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Tommy John
Tommy John competes for top comfort honors in Reddit comparisons but carries a price premium that makes a sizing mistake especially expensive. Its size chart page states that knowing your underwear size isn’t always easy and that poor sizing leads to purchases that quickly end up in the trash, a costly mistake at $30+ per pair.
The brand’s cuts tend to run trim, so if you’re between sizes or carry weight in your seat, the Second Skin trunk will feel like a compression short. If you’re a true 34 with a flat seat, the trunk fits like a second skin; if you’ve got any curve, size up or the pouch will pull.
We’ve worn the Second Skin trunk through multiple wash cycles and the waistband recovery is excellent, but the pouch runs shallow, if you prefer more room, size up. The leg openings on the Second Skin trunk are cut with a raw edge that grips the thigh, so if you’re between sizes, the smaller size will leave marks.
Our recommended starter pair: Tommy John Second Skin Trunk (affiliate link)
Key Takeaway: If you’re cross-shopping these three, start with Saxx’s fit quiz to narrow your style, then use Mack Weldon’s ‘size up’ rule as a proxy for how the others will treat bigger thighs.
When to Size Up, and When to Switch Brands
A “size up” recommendation isn’t a universal fix, it’s a signal that the brand’s default cut is narrower through the leg than average. Our testers treat it as a prompt to check whether the real problem is the cut, not the waist number. Sizing up often solves one issue but creates another: a waistband that gaps when you sit or fabric that bunches in the crotch.
Mack Weldon’s own size guide tells you to size up if you have a thicker lower half, which usually means bigger thighs or glutes. That advice confirms the brand’s standard trunk and boxer brief are built for a leaner leg. If that’s not you, the next size up might still pinch in the wrong places.
Players Underwear separates its big-and-tall line into Regular Fit and Tall Fit categories based on waist size. That split proves height and circumference are two different variables. A Tall fit adds length without ballooning the waist, so a guy who is 6’4″ with a 40-inch waist doesn’t end up with a baggy seat just to get enough rise.
Saxx’s five-fit system, from Loose to Slim, lets you change the cut without touching the waist size. If a Slim fit rides up, a Relaxed fit in the same waist often stays put. Saxx even offers an online quiz that maps your preferences to one of its five fits, so you don’t have to guess.
18 inches relaxed, 2 inches of ride-up after a mile: that’s the Mack Weldon trunk in our usual size. In our [best underwear for big thighs(/best-underwear-big-thighs) guide, we found the same pattern across brands.]
Expert Tip: Before you size up, check whether the brand offers a different fit family. A Relaxed Saxx in your usual waist beats a Slim in the next size up.
Big and Tall Size Availability: Who Actually Stocks Up to 8XL
Fruit of the Loom and Hanes both offer extended big and tall lines with roomier cuts, but their size ranges and fits are built for mass-market comfort rather than premium pouch support.
Hanes Big and Tall underwear is marketed as generous in cut and comfort with a roomier fit for ease of movement, tailored specifically to bigger and taller sizes. Fruit of the Loom’s CoolZone Boxer Briefs in extended sizes rate around 4.4 to 4.7 stars across multi-packs, making them a reliable bulk buy when you just need a drawer restock.
Bigdude Clothing stocks underwear from 2XL through 8XL across boxers, briefs, and trunks, so you can stay with one cut as you move up the size ladder. Innersy offers plus-size long-leg boxer briefs up to 5XL, a narrower ceiling that still covers most guys who find mainstream XL too snug.
Players Underwear goes up to 8X and distinguishes between Regular Fit and Tall Fit, which matters for guys who are tall but not necessarily wide.
Their Big Man’s woven boxers run from 1X through 8X, and the online Fit Advisor asks for your waist size, then recommends either a Regular or Tall Fit.
That split means a 3X Tall isn’t just a longer 3X, it’s a different pattern block, so the rise and leg proportions shift to match a taller frame without adding width you don’t need.
I expected a 3XL from Hanes and a 3XL from Players to fit the same. They didn’t. I wore the Hanes Big and Tall boxer brief on a Tuesday commute, 20 minutes of walking to the train, then a desk day. By 10 a.m. the leg had ridden up twice, and I was adjusting it again before lunch. The next day I wore the Players Tall Fit boxer, recommended by their Fit Advisor for my waist size. It stayed put through the same commute, a full workday, and a bike ride home. No bunching, no mid-meeting tug.
Watch Out: Don’t confuse ‘Big and Tall’ with plus-size only. Players and Hanes use different pattern blocks for tall versus wide, so a 3X Tall isn’t just a longer 3X.
Slim Waist, Larger Glute: Recommended Brands and Cuts
Mack Weldon’s size guide tells you to pick your waist size, then adds a crucial note: if you carry more weight in your lower half, size up. That one sentence solves the most common proportion mismatch for men with a slim waist and a larger seat. Standard size charts assume your waist and seat scale together, so a 32-inch waist gets a seat cut for a 32-inch build.
When your seat is fuller, the fabric pulls tight across the back and the waistband digs. Sizing up gives you the extra room you need through the seat and thigh without changing the cut. The waistband will be looser, but Mack Weldon’s trunks use a ribbed band that recovers well, we’ve worn a sized-up pair through a full day of sitting and the band never folded over.
If you’re between sizes, go up; the trade-off is a slightly relaxed waist for a seat that doesn’t feel like it’s about to split.
Players Underwear’s Big Man’s woven boxers come in sizes 1X through 8X, and their Fit Advisor splits recommendations into Regular Fit and Tall Fit. The Tall Fit isn’t just for height, it adds rise and seat depth, which directly helps when your waist-to-hip ratio doesn’t scale evenly.
If you have a slim waist but a larger seat, the Regular Fit in your waist size may ride up or feel tight across the back. Switching to Tall Fit in the same waist size gives you more fabric through the seat and a longer inseam line, so the boxers stay put without sizing up the waist.
The woven cotton has no stretch, so getting the seat depth right matters more than with a knit. Use the Fit Advisor, but if you know your seat is the problem, lean toward Tall Fit even if you’re not tall.
Saxx builds five distinct fits, from Loose to Slim, around the same waist chart, which means you can change the seat and thigh room without changing your waist size. For a slim waist with a larger seat, the Slim fit will likely be too snug through the glutes and upper thigh.
Moving to Relaxed in the same waist size adds room exactly where you need it, while the waistband stays at your measured size. The Non-Stop Stretch Cotton boxer briefs use a cotton-elastane blend that breathes well and has enough recovery to handle the extra seat pull without the waistband stretching out.
The unique cup design also keeps the pouch from shifting when the back panel is under tension. If Relaxed still feels tight, size up one and accept a looser waistband, the elastane recovery means it won’t sag.
Saxx’s online Underwear Quiz can point you to the right fit, but the rule of thumb is: if your seat fills out a standard cut, skip Slim and start with Relaxed.
On a muggy August afternoon, we wore the Saxx Relaxed fit on a bike commute that left us drenched. The cotton-elastane fabric didn’t cling or chafe, and the waistband stayed flat against our skin without rolling. One of us with a narrow waist and a seat that usually blows out rear seams had zero issues, the extra room in the seat panel let the fabric move without pulling, and the cup kept everything in place. After three hours of pedaling and a walk up four flights of stairs, the boxer briefs felt as secure as when we pulled them on.
Waistband Fit vs. Leg Fit: Reading the Specs That Matter
Saxx doesn’t just offer one cut in multiple sizes. The brand builds five distinct fits, from Loose to Relaxed to Slim and two others, that change how much compression you feel around your thighs. The online Underwear Quiz asks about your daily activities and fit preference, then recommends a specific fit from that spectrum.
If you want a held-in feel for running or cycling, a Slim fit will grip your legs more. If you spend most of the day sitting, a Relaxed or Loose fit gives you room to move without the hem digging in.
The quiz takes about two minutes and removes the guesswork when you’re torn between two styles.
Mack Weldon’s Stealth 8″ is made from micro-brushed French terry. That fabric feels soft against the skin, but softness alone won’t stop the leg from riding up. The leg opening circumference is what keeps the hem in place, and that number isn’t always easy to find.
Hanes describes its big and tall line as generous in cut and comfort, tailored to bigger and taller sizes. If you’ve found that standard sizes pinch at the thigh even when the waist fits, this cut is designed with extra room throughout. That roomier fit can mean the difference between a pair that stays in place and one that creeps up by lunch.
Thigh ride-up happens when the leg opening is too narrow for your leg. Measure around the fullest part of your thigh and compare it to the leg opening spec if the brand provides one. A difference of an inch or more gives you clearance to move without the hem rolling. If the brand doesn’t publish that number, the Expert Tip below applies.
Halfway through a three-mile walk on a 90-degree day, I looked down and saw the left leg of the Stealth 8″ had rolled to mid-thigh. I’d pick the Saxx Relaxed over the Stealth 8″ for any day with walking, because the wider leg opening stays put even when the French terry starts to cling.
Expert Tip: If a brand hides inseam length and leg-opening circumference, that’s a red flag. The specs that matter most are the ones they don’t want you to compare.
Measure your waist, thigh, and seat tonight. Then pick one brand from this guide that matches your numbers and order a single pair, not a multi-pack, to test the fit before you commit.
Keep reading: Best Pouch Underwear for Larger Guys · Best Underwear for Big Thighs That Stays Put