How Do I Find My Size in Mom Jeans?

By Ella Blake, Tellar Stylist

To find your size in mom jeans, measure your natural waist and hips, then size up by one — because the high-rise, relaxed cut of a mom jean fits very differently to a skinny or straight-leg style, and going in with your usual number is one of the most common (and most frustrating) mistakes you can make.

I learnt this the hard way. I picked up what looked like an absolutely perfect pair — the ideal vintage wash, just the right amount of taper — in my usual size 12. Reader, I could not get them past my thighs. The thing about mom jeans is that they're cut wide through the seat and thigh but often have very little stretch. They can look roomy hanging on a rail and then be completely unforgiving on an actual human body. So let's get you sorted properly.

Why Mom Jeans Fit Differently

Most contemporary jeans — your skinnies, your jeggings, your stretch straight-legs — contain a healthy percentage of elastane. Mom jeans, particularly the more authentic vintage-inspired styles, are often made in rigid or near-rigid denim with very little give. That changes everything.

The high rise means they sit at or above your natural waist, which is almost always narrower than your hips. This creates a natural size conflict — what fits your waist can pull across the hip, and what fits your hip can gape at the waist.
The relaxed thigh is roomy by design, but the cut varies enormously by brand. Some are genuinely relaxed; others are only slightly looser than a straight leg.
The taper at the ankle can make the leg feel tighter than the numbers suggest, especially if you're curvier through the calf.

How to Measure Yourself Correctly

Before you buy a single pair, grab a soft tape measure. You want two key measurements:

Natural waist: Measure around the narrowest part of your torso — usually an inch or two above your belly button. Don't suck in, don't hold your breath. Just stand naturally.
Hips: Measure around the fullest part of your hips and bottom — usually about 8–10 inches below your natural waist.

Now, use your hip measurement as your primary guide when choosing a size in mom jeans. The waist can almost always be taken in with a belt or a simple alteration. Hips cannot.

Sizing by Brand — What You Need to Know

This is where it gets interesting — and honestly, quite maddening — because sizing across the high street varies enormously. Here's my honest breakdown of where to shop and what to expect:

Levi's are the gold standard for mom jeans and their 501 and 80s Mom styles are sized by waist and inseam in inches, not UK sizes. A UK 12 is roughly a 29W. Always size up one waist size if you're between measurements — their denim is stiff and does not stretch.
Mango cuts their mom jeans quite small through the hips — I'd go up one full UK size from your usual. Their washes are gorgeous though, and the quality for the price is excellent.
Zara mom jeans are inconsistent across styles — some run true to size, others come up small. Check the fabric content: if it's 98%+ cotton, size up. If it has some elastane, you might be fine with your usual.
ASOS is brilliant for this style because they carry their own brand plus dozens of labels, and the detailed size guides and customer reviews make it much easier to navigate fit before you buy.
Topshop (now via ASOS) Mom jeans have a loyal following for good reason — they're cut generously through the hip and the waist band is flattering at a high rise. Generally true to size.
Abercrombie & Fitch have become the unlikely darlings of the mom jean world — their '90s Relaxed' fits are incredibly well-cut, run true to size, and come in a wide range of inseam lengths.
M&S mom jeans are a solid, underrated option — particularly if you're between a UK 14 and 18. Their per una and straight-cut mom styles are generous, comfortable, and often have a touch of stretch.
Citizens of Humanity are at the premium end but absolutely worth the investment if you find the right pair. Their Liya and Marlee styles are cut for women with curves — roomy through the hip, tapered cleanly at the ankle.
Paige denim fits beautifully and uses high-quality stretch denim even in their relaxed styles. Generally true to size and more forgiving than rigid options.

For two more brilliant independent options, I love Boyish Jeans — a sustainable denim label making incredibly flattering mom and relaxed styles — and Agolde, whose '90s Pinch Waist' cut is one of the most universally flattering high-rise jeans I've ever come across. Both have detailed fit guides on their sites.

Common Fit Problems and How to Fix Them

Gaping at the back waistband: Very common with mom jeans if you have a smaller waist relative to your hips. A good tailor can take this in for around £15–20, or use a wide belt to cover it.
Too tight across the thigh: Go up a size and belt the waist. The thigh cannot be let out; the waist can always be adjusted.
Too long in the leg: Mom jeans are supposed to sit at ankle length — a slightly cropped, straight finish. Most styles come in a 28" or 30" inseam. If you're petite, the 28" is your friend.
Bunching at the knee: This usually means the thigh is too wide for your frame. Try a slimmer-cut mom style or a straight-leg instead.

One Last Tip — Buy Two Sizes and Try

If you're shopping online (which most of us are), order two sizes if you're unsure. The cost of return postage is far less frustrating than settling for a pair that doesn't quite fit. Mom jeans are a wardrobe staple — when they're right, they're really right — so it's worth taking the time to find your perfect pair rather than pushing through with something that's almost there.

Never Guess Your Size Again — Try Tellar

Sizing in mom jeans is tricky precisely because every brand cuts differently. That's exactly why Tellar.co.uk exists — it's the UK's leading free sizing tool, matching your exact measurements to over 1,500 brands instantly. No more guessing, no more disappointing returns.

Measure once — bust, waist and hips — and Tellar does the rest.
Use the Store Size Lookup tool to find your precise size in any brand — Levi's, Citizens of Humanity, ASOS, Zara and hundreds more.
It's always free — no app download, works straight in your browser.

And while you're there, don't miss the Tellar Fashion Hub — a library of honest, unbiased, stylist-written posts covering everything from fabric guides to body shape advice. Start with the Ultimate Clothing Sizing Guide, or explore the Best Jean Trends for 2026, the Ultimate Guide to Dresses, and the Ultimate Guide to Jackets. No ads. No sponsors. Just genuinely useful advice.