ASICS vs Nike Sizing: Do They Fit the Same? (Men & Women 2025 Guide)

You want a straight answer before you hit “add to cart.” Are ASICS and Nike the same size? On the label, mostly yes. On your feet, not always. Both brands use the same US/EU numbering for length, and both say a men’s US 9 equals 27.0 cm and a women’s US 8 equals 25.0 cm. But last shape, toe box volume, and midfoot hold can make one brand feel shorter or longer in real life, even at the same printed size. If you just want to run tonight without heel rub or black toenails, here’s the fast, no-nonsense playbook.

TL;DR and Quick Answer

Key takeaways

• No, they don’t always fit the same. The number on the label often matches, the on-foot feel can differ by model.
• Use your foot length in cm as the anchor. For both brands, men’s US 9 ≈ 27.0 cm; women’s US 8 ≈ 25.0 cm (per ASICS and Nike official size guides, 2025).
• If you’re between sizes or wear thick socks/orthotics, half-size up-especially for long runs or races.
• Widths matter: ASICS offers more width options across stability/daily trainers; Nike offers widths in select models only.
• Fit changes by model: Pegasus ≈ true to size; Vaporfly/Alphafly feel snug; ASICS Nimbus/Novablast roomy forefoot; Kayano locked-in midfoot.

What you came here to do (jobs-to-be-done):

• Decide if your Nike size equals your ASICS size, or if you need to go up/down.
• Convert size using a reliable method you can trust (cm-based, not guesswork).
• Account for width, socks, insoles, and swelling on long runs.
• Pick the right size for popular models (Pegasus, Vaporfly, Kayano, Nimbus, Novablast).
• Avoid returns by following a quick fit check at home.

60-second decision tree:

1. Measure your foot length in cm (both feet; use the longer one).
2. Match that cm to the brand’s size guide: 0.0/0.5 cm steps-don’t round down.
3. Wide feet/orthotics/high mileage? Go up 0.5 US.
4. Racing shoe or narrow last? Consider +0.5 US if you’re near the threshold.
5. Check width availability: ASICS (more options), Nike (select models).

Who am I to say? I’m a Melbourne runner who rotates both brands year-round, and I’ve helped plenty of club mates avoid that awkward half-size dance at the store. The notes below are the patterns that keep showing up, paired with what the brands’ 2025 size charts actually say.

How to Nail Your Size Across ASICS and Nike

Start with the one metric both brands agree on: foot length in centimeters. Don’t rely on your “usual size.” If you’ve never measured properly, do it now-it takes two minutes and saves you two returns.

Home measurement (accurate enough to buy online):

1. Tape a sheet of paper to the floor flush against a wall.
2. Stand with your heel gently touching the wall, weight distributed evenly.
3. Mark the tip of your longest toe. Measure from wall to mark in centimeters.
4. Measure both feet. Use the longer measurement.
5. Add 0.5-1.0 cm “run room” for training shoes; 0.3-0.5 cm for racing if you like a snug feel.

What the brand charts say (2025, men’s/women’s):

• ASICS: Men’s US 9 = 27.0 cm; Women’s US 8 = 25.0 cm (ASICS Official Size Guide, 2025).
• Nike: Men’s US 9 = 27.0 cm; Women’s US 8 = 25.0 cm (Nike Size Guide, 2025).

So why do they sometimes feel different? Shape. ASICS often builds a slightly more structured midfoot in stability shoes and gives generous volume in certain daily trainers (Nimbus, Novablast). Nike’s daily trainers like Pegasus run true for many, but their racing line (Vaporfly/Alphafly) leans snug and shallow through the forefoot. A 27 cm foot in a US 9 might feel roomy in one model and tight in another. Label length = same, but volume and last geometry ≠ same.

Rules of thumb I actually use:

• Daily trainers: Stick with your true US size for both brands if the chart puts you comfortably within that cm band.
• Racers/tempo shoes: If you’re on the cusp, go +0.5 US, especially in Nike Vaporfly/Alphafly or ASICS Metaspeed if your forefoot is wide.
• Wide feet: Try width options first. If unavailable, +0.5 US can help, but watch heel security.
• Orthotics or high-volume socks: +0.5 US, and aim for 0.5-1.0 cm of front space.
• Long runs in summer: Feet swell. Err on the roomier side (+0.5 US) to save your toenails.

Width options at a glance:

Model-by-model tendencies (2024-2025 updates):

• Nike Pegasus 41: True to size for most. Medium forefoot, secure heel. If you like thick socks, +0.5 US for comfort.
• Nike Invincible Run 3/Run (latest): True to size but high-volume upper; wide feet often happy at true size.
• Nike Structure/InfinityRN: True to size; moderate midfoot hold. Try wide if you need forefoot space.
• Nike Vaporfly 3/Alphafly 3: Snug mid/forefoot. Many runners go +0.5 US unless they prefer a locked, racing fit.
• ASICS GEL-Nimbus 26: True to size with a roomier toe box than older Nimbus; high comfort, forgiving volume.
• ASICS Novablast 4: True to size; fair toe-box room. Narrow feet may prefer thick socks or heel lock lacing.
• ASICS GEL-Kayano 31: True to size with secure midfoot; consider wide (2E men/D women) if your forefoot spreads on long runs.
• ASICS GT-2000 12: True to size; medium volume. Reliable for orthotics at true size or +0.5 US if high-volume insert.
• ASICS Metaspeed Sky/Edge: Performance fit. Many size up 0.5 US for marathon distance.

AU, US, UK size notes (Melbourne-friendly):

• Most running shops in Australia list US sizes on the box and shelves.
• Men’s UK size is typically 1 down from US (US 10 ≈ UK 9). Women’s conversions vary more; check the label.
• If a site shows “AU,” it’s usually the same as US for athletic shoes. When in doubt, follow the cm metric.

Why cm beats guessing: Both ASICS and Nike base their charts on foot length in centimeters. If your foot is 27.0 cm, you anchor at US 9 in both. The difference is how each last holds your foot. That’s why two US 9s can feel different.

If you only remember one thing: pick your size by cm first, then adjust by 0.5 up or down based on width, socks, orthotics, and whether the shoe is a racer or a daily trainer.

Examples, Comparisons, Checklists, and Your Next Steps

Let’s put it into practice. Here are real-world scenarios that match how people actually buy shoes.

Scenario A: You wear Nike Pegasus 41 in men’s US 10, medium socks, daily easy runs.

• Foot length: likely around 28.0 cm.
• ASICS Nimbus 26/Novablast 4: Try US 10 as well. If you feel sloppy in Pegasus at day’s end, go US 9.5 in ASICS; if you want wiggle room for long runs, stick with US 10.
• ASICS Kayano 31: Start at US 10; if forefoot feels snug late in the run, US 10 Wide (2E) can be perfect without changing length.

Scenario B: You race in Nike Vaporfly 3 women’s US 8, but toes feel pressed at 30 km.

• Foot length: around 25.0-25.5 cm.
• Try women’s US 8.5 in Vaporfly/Alphafly, or US 8.5 in ASICS Metaspeed for more breathing room. Minimal penalty in lockdown, major gain in comfort.

Scenario C: You have a wide forefoot and neutral gait, men’s foot length 27.0 cm.

• ASICS: Nimbus/Novablast often feel accommodating in standard D. If needed, go 2E wide at the same length (US 9).
• Nike: Check if your model offers 2E. If not, +0.5 US in a roomy daily trainer (e.g., Invincible Run) can solve pressure without heel slip.

Scenario D: You use custom orthotics.

• Start with your cm-based true size.
• Test the in-shoe volume with the orthotic inserted. If the upper presses on the top of your foot, go +0.5 US or choose a model with a taller toe box (Nimbus, Pegasus).

Scenario E: Hot weather long runs (hello, Aussie summer).

• Feet swell more. If you’re borderline between sizes, favor +0.5 US for your long-run trainer.

Quick comparison table (fit feel, not just the label):

Cheat-sheet (save this):

• Pick by cm first, not by “my usual.”
• Daily trainer: true size; race shoe: often +0.5 US.
• Wide feet? Use width options if offered before changing length.
• Orthotics/thick socks/hot days: +0.5 US.
• At-home fit test: standing thumb test, downhill jog, heel slip check.

At-home fit test (2 minutes):

1. Length: While standing, you want about a thumb’s width (0.5-1.0 cm) in front of the longest toe for training shoes.
2. Width: No hot spots or numbness after 5-10 minutes of wear. Wiggle toes freely.
3. Heel: Minimal slip. If heel lifts, try runner’s loop lacing before swapping sizes.
4. Downhill test: On a stair or ramp, toes shouldn’t slam the front. If they do, size up or adjust lacing.

Mini-FAQ

• Are ASICS and Nike US sizes the same on the label? Yes. Both say men’s US 9 = 27.0 cm; women’s US 8 = 25.0 cm (brand size guides, 2025).
• Why does one feel tighter? Different last shapes and toe box depth. Same label length, different volume.
• Should I convert by EU size? EU numbers are close but not identical across brands. Use cm; it’s more precise.
• What about UK/AU sizes? In Australia, shops mostly list US sizes. Men’s UK is roughly US minus 1. Still, follow cm.
• I’m between sizes. Go up or down? For running, go up 0.5 US more often than down, unless you want a snug race fit.
• Do ASICS run narrow? Stability models can feel more locked. Daily trainers like Nimbus/Novablast are often roomy. Choose widths if needed.
• Do Nike racers run small? They run snug. Many runners take +0.5 US for marathon distance comfort.
• Kids’ sizes? Same idea-measure in cm and match the chart. Don’t buy tight; leave growth room.

Common pitfalls to avoid:

• Buying by past size. Your feet change with training volume and age.
• Ignoring socks. A thick cushioned sock can eat 0.5 cm of space.
• Assuming all models in a brand fit the same. They don’t.
• Believing a shoe “will break in.” Length won’t. If it’s short, it stays short.

Pro tips from the road:

• Lacing tweaks can fix heel slip without changing size (runner’s loop, window lacing over pressure points).
• If your second toe is longer, size off that toe, not the hallux.
• Marathoners: Aim for 0.5-1.0 cm space at the end of long runs, when feet are warm and swollen.
• Orthotics users: Remove the stock insole before inserting your orthotic. Re-check volume standing.

Real conversions (based on cm, not guesswork):

• Men’s 27.0 cm foot: Start at US 9 in both brands. If Vaporfly/Alphafly feels tight, try US 9.5. Nimbus/Novablast often fine at US 9.
• Women’s 25.0 cm foot: Start at US 8 in both. For Metaspeed/Vaporfly long races, consider US 8.5 if toes brush at the front.
• Men’s 28.5 cm foot with orthotics: US 10.5 baseline; in Kayano/Structure, same length with wide option if available; otherwise US 11 for volume.

Returns and try-on strategy (so you don’t lose time or money):

• Order two sizes (true and +0.5) if the retailer offers free returns. Try both on carpet, late afternoon.
• Keep the one with proper length + width comfort + heel security. Walk, jog in place, test stairs.
• In-store? Bring your race socks and orthotics. Don’t test in thin ankle socks if you’ll race in thick ones.

Why this advice holds up: Both brands publish cm-based charts that align in the middle sizes, but shoe geometry changes the feel. That’s why runners in Melbourne-and pretty much anywhere-can swap brands at the same label size and still prefer a half-size change in certain models. Charts match; last shapes differ.

Bottom line you can act on today: find your cm, pick that US size in both brands, then nudge 0.5 up if you’re wide, you add orthotics, or you’re buying a snug racer. That solves 90% of fit issues between ASICS and Nike.

Oh, and if you see the phrase Asics vs Nike sizing floating around forums, remember it’s not a fight about the number-it’s a conversation about shape. Use the number to get in the ballpark; use shape knowledge to get the perfect fit.

Sources used for the specifics above: ASICS Official Size Guide (2025), Nike Size Guide (2025), plus repeated on-foot testing in Nimbus, Novablast, Kayano, Pegasus, Invincible, Vaporfly, Alphafly, and Metaspeed models across recent seasons.