You order a medium from one site, a medium from another, and somehow only one of them fits. That’s not you doing anything wrong. Clothing sizes were never standardized across brands in the first place, and H&M and Old Navy are a good example of just how differently the same label can behave.
Both brands sell women’s clothing, jeans, dresses, basics, petite pieces, and extended sizes. Neither sizes them the same way. This guide breaks down how each brand actually approaches sizing, where the real differences show up, and how to convert between the two without just guessing and hoping.
If you’re weighing the two brands more broadly, not just on fit, our H&M vs Old Navy quality comparison covers fabric, durability, and value.
The Short Answer: Neither Brand Runs Consistently Bigger or Smaller
It would be convenient if one brand simply ran a size larger across the board. It doesn’t work that way.
| Category | H&M | Old Navy |
|---|---|---|
| Sizing system | Mostly per-product; check each item’s own size guide | Broad numeric and letter sizing, fairly consistent site-wide |
| Jeans | Waist/inseam labeled, varies by cut | Numeric sizing plus Regular, Petite, and Tall options on many styles |
| Petite | Built into some product proportions rather than a separate size | A clearly labeled Petite option on most jeans and many other pieces |
| Plus sizes | A dedicated plus collection; availability varies by item | A wide plus range, especially strong in denim |
| Best strategy | Read the size guide on the actual product page | Compare your measurements against the specific style’s chart |
The mistake almost everyone makes is treating a size label as if it converts one-to-one between brands. It doesn’t. Even within one brand, it can shift from item to item.
How Old Navy Sizing Works
Old Navy leans on both letter sizing (XXS through XXL) and numeric sizing, depending on the product, plus a genuinely broad plus range. The brand has built its whole approach around size-inclusive shopping: women’s sizing runs roughly 00 through 30 and XS through 4X, generally offered as one continuous range rather than a separate “plus” section tucked away elsewhere on the site.
Reading the Label: Letter vs. Numeric
Don’t assume a numeric size (say, a 10) automatically lines up with a specific letter size (a Large) across every style. Old Navy’s customer service and sizing resources are worth a look, but the individual product page is still the more reliable source, since the same numeric size can sit in a different letter range depending on the cut and category.
Jeans: Where It Gets More Interesting
Jeans are the category with the most moving parts. Beyond the waist number, Old Navy varies:
- Rise (low, mid, high)
- Leg shape (straight, loose, slim, bootcut)
- Inseam length, usually offered as Regular, Petite, and Tall
- Denim weight and stretch
Two jeans with the same waist size can fit completely differently depending on these. A straight-leg pair and a loose pair might share a waist measurement but feel nothing alike through the hip and thigh.
Should you size up? It depends on the denim, not a blanket rule. Rigid, non-stretch denim tends to fit snugger with essentially zero give, so a lot of shoppers do size up for comfort. Stretch denim is more forgiving and usually fits true to your regular size. Read the fit description on the product page before deciding either way.
For a closer look at how jeans sizing plays out at a different budget-friendly retailer, our Maurices bootcut jeans sizing guide walks through a lot of the same rise-and-leg logic.
Petite and Tall Options
Old Navy offers Petite and Tall as fit categories across a wide range of jeans and other clothing, not just a shortened or lengthened version of Regular. Petite adjusts rise, inseam, and overall proportions for shorter frames; Tall does the opposite. If you’re a size 6 in Regular, it’s worth checking whether Petite 6 or Tall 6 actually fits better through the torso and legs, rather than assuming Regular is the default correct choice.
The same logic extends to dresses, jumpsuits, and other one-piece styles, where torso length matters as much as size. Our Old Navy jumpsuit sizing guide gets into exactly this — where the brand’s sizing tends to run generous or tight depending on the style.
Plus Sizes at Old Navy
Old Navy’s plus range is one of its clearer strengths, particularly in denim: multiple fits, multiple inseam options, and sizing that extends well beyond what a lot of competitors offer. If you’re shopping plus-size jeans specifically, pay close attention to waist and hip measurements together, since the same numeric size can feel different across a slim, straight, bootcut, or loose cut.
How H&M Sizing Works
H&M takes a more product-by-product approach. Rather than publishing one universal chart and expecting every item to match it, H&M’s own guidance is to open the specific product page and use the Size Guide listed there, since fit and measurements can vary from one garment to the next.
Why “Medium” Doesn’t Mean Just One Thing
A letter size at H&M is a label, not a guarantee. A fitted top and an oversized sweatshirt can both be tagged M and fit completely differently. The brand’s size charts are built around body measurements: bust, waist, hips, and inner leg, so those numbers are worth having on hand before you buy anything fitted. Dresses are where this matters most. A fitted or bodycon style is safest sized to your largest measurement, usually bust or hips, while a loose or A-line dress gives you more room to size down comfortably.
Jeans: The Waist/Inseam Format
H&M jeans are commonly labeled in a waist/inseam format, something like 30/32, where the first number is your waist in inches and the second is the inseam. That’s a more precise system than a single letter size, but it still only tells part of the story. A high-rise skinny cut and a relaxed wide-leg pair can share a waist measurement and fit nothing alike everywhere else. Check the fit description (slim, straight, wide-leg, relaxed) alongside the numbers.
Petite Proportions
H&M’s approach to petite sizing isn’t a separate “P” label so much as adjusted proportions built into the sizing itself, aimed at improving sleeve, torso, and leg length for shorter frames. If you’re petite, the practical move is checking a garment’s actual length details rather than hunting for a specific petite tag.
Plus Sizes at H&M
H&M runs a dedicated plus-size collection, with sizing extending up to 4XL on selected items. Availability isn’t uniform across every category, though, so it’s worth checking a specific product’s available range before assuming your size is in stock.
Bra Sizing Needs Its Own Measurement
Bra sizing is really its own category, separate from everything else. H&M’s guidance is to measure directly under the bust to work out your band size and combine that with your usual bust measurement for cup size. Your regular clothing size isn’t a substitute for actually measuring.
Head-to-Head: Which Brand Handles Sizing Better?
There’s no universal winner. It depends on what you’re buying and what matters most to you.
For jeans and denim, Old Navy has a slight edge simply on convenience. Numeric sizing combined with Regular, Petite, and Tall options across a wide range of styles gives you more direct ways to land on the right fit without guesswork.
For petite shoppers, Old Navy’s clearly labeled Petite filter is easier to shop by. H&M can still work well, but you’ll need to check garment measurements rather than relying on a label to do the work for you.
For plus sizes, both brands offer solid ranges, but they lean differently. Old Navy’s plus strength is really in denim specifically. H&M’s plus collection covers more fashion-forward pieces, tops, and dresses, though availability varies more by item.
A Better Way to Convert Between the Two
Skip trying to memorize a conversion chart. Use this instead:
- Measure yourself. Bust, waist, hips, and inseam — actual body measurements, not the size on a tag you already own.
- Check the specific product’s chart. Old Navy’s numeric sizing or H&M’s individual product size guide, whichever applies.
- Read the fit description. Slim, relaxed, oversized, stretch, and rigid all change how the same number feels.
- Skim a few reviews. “Runs small,” “true to size,” and “tight through the hips” tell you more than the size chart alone.
- Know the return policy before you order. If you’re between sizes, it’s worth knowing your options going in rather than after the package arrives.
Common Sizing Mistakes Worth Avoiding
A few habits cause more fit problems than the actual size charts do:
- Carrying your size from one brand straight to the other. A 10 at Old Navy and a 10 at H&M aren’t guaranteed to match.
- Sizing by height alone. Height affects length, not how something fits around your waist, hips, or bust.
- Ignoring the inseam. Two jeans with an identical waist can look completely different depending on the leg length.
- Ignoring stretch. Rigid denim and stretch denim can call for different decisions even at the same labeled size.
- Assuming plus sizing is identical across retailers. It isn’t, even between two brands that both offer a wide range.
Frequently Ask Questions
Does Old Navy run big or small?
It varies by product. Some styles run generous, others fit closer to the body. Checking the specific item’s fit description matters more than a general rule.
Is H&M sizing smaller than Old Navy?
Not consistently. It depends on the garment, fabric, and collection, so measurements are more reliable than assuming either brand runs small or large across the board.
Should I size up in Old Navy jeans?
Only if the style is rigid, non-stretch denim. Stretch styles generally fit closer to true to size.
Is H&M medium the same as Old Navy medium?
Not necessarily. Letter sizes aren’t standardized between brands, so compare actual measurements rather than assuming.
Which brand is easier to shop for plus-size jeans specifically?
Old Navy currently has the broader plus-size denim selection, with more fit and inseam combinations to choose from.
Final Verdict
Neither brand is universally bigger, smaller, or more accurate than the other. Old Navy’s strength is breadth: numeric sizing, Petite and Tall options, and an especially wide plus-size jeans range. H&M’s strength is precision at the product level, with detailed size guides built around actual body measurements rather than one generic chart.
The practical takeaway is the same either way: measure yourself once, check the specific product’s chart, and read the fit description before you buy. That works better than assuming your usual size will translate.
For more on how the two brands compare beyond fit, H&M vs Old Navy: Which Brand Has Better Quality? covers fabric and durability. And if you’re sizing up jeans or basics from other budget-friendly brands too, our Maurices review works through a lot of the same fit questions from a different angle.
