adidas Ultraboost 20 fits true to size for most people — the same number as Air Jordan 1, Air Max 90, and YEEZY Boost 350 V2, and about half a size larger in number than your Air Force 1. The Primeknit+ upper and heel counter hold the foot at length; the Boost midsole compresses slightly with wear. Based on 351 owner-reported pairs in the Feetlot database, the typical wearer takes the same number in Ultraboost 20 as in any other Ultraboost generation. If unsure: order true to size. Wide feet should size up half — the heel counter doesn't flex.
Ultraboost 20 Sizing — What 351 Pairs in the Feetlot Database Tell Us
The adidas Ultraboost 20 is the 2020 generation of the Ultraboost line. Across 351 owner-reported pairs, the residual variance is tight (standard deviation ≈ 0.24 size units), consistent with all prior Ultraboost generations. Feetlot data shows UB 20 fits true to size — the same number as AJ1, Air Max 90, and Vans Authentic, and about half a size larger in number than AF1. All Ultraboost generations from 1.0 through UB 21 sit in the same size bucket.
The Ultraboost 20 introduced the Primeknit+ upper — a denser, more supportive knit than the 4.0's Primeknit — and a revised heel frame that connects the upper to the outsole with a single piece of thermoplastic. Like all Ultraboost generations, the heel frame holds the foot at length; the Primeknit+ sits close to the foot without AF1's heel slack.
Should You Size Up or Down in Ultraboost 20?
Standard fit (most people)
Order true to size — your usual sneaker number (AJ1, AM90, SB Dunk Low, Vans Authentic). Don't apply a half-size-down adjustment just because AF1 is your reference shoe. AF1 runs half a size smaller in number than UB 20; they're not the same size.
Wide feet
Size up half. The Primeknit+ is slightly less stretchy than the classic Primeknit, so the UB 20 may feel snugger at the forefoot for wide feet than earlier Ultraboost generations. Half a size up is the standard wide-foot adjustment.
Narrow feet
True to size works for most narrow feet. The Primeknit+ holds the foot regardless of width. Going half down risks heel slip inside the frame.
Ultraboost 20 vs Ultraboost 21 and Later
Ultraboost 20 and the Ultraboost 21 (2021) use the same last and the same length advice — true to size. The 21 introduced a redesigned heel frame that reduces the frame-induced "grip" feeling some wearers noticed in the 20. Same size between them.
How Ultraboost 20 Compares to Other Sneakers
The adidas Ultraboost 20 fits at the same numerical size as Air Jordan 1, Air Jordan 3, Air Jordan 4, Air Jordan 5, Air Jordan 6, Air Jordan 11, Nike Air Max 90, Nike Air Max 1, Air Max 95, Air Max 97, Air Max 270, Nike Dunk Low, Nike Dunk High, SB Dunk Low, Nike Blazer Mid '77, Vans Authentic, adidas NMD R1, adidas YEEZY Boost 350 V2, and New Balance 574. According to Feetlot data, all of these round to the same size in 0.5 increments.
The shoes that run larger in number than Ultraboost 20: Nike Air Force 1 runs about half a size smaller in number — if you wear AF1 in 10, take UB 20 in 10.5. Converse Chuck Taylor Ox and Sperry Authentic Original also run about half a size smaller. Clarks Desert Boot runs about half a size smaller in number as well.
Boot-style models: Red Wing Iron Ranger runs about a full size smaller in number than UB 20 — if you wear UB 20 in 10, take Iron Ranger in 9.
Sign in to Feetlot and add a few of your other sneakers to get a personal Ultraboost 20 size recommendation calibrated to your actual foot.
adidas Ultraboost 20 Size Chart (US / EU / UK)
| US Men's | US Women's | UK | EU |
|---|---|---|---|
| 7 | 8 | 6.5 | 40 |
| 7.5 | 8.5 | 7 | 40.5 |
| 8 | 9 | 7.5 | 41.5 |
| 8.5 | 9.5 | 8 | 42 |
| 9 | 10 | 8.5 | 43 |
| 9.5 | 10.5 | 9 | 43.5 |
| 10 | 11 | 9.5 | 44 |
| 10.5 | 11.5 | 10 | 44.5 |
| 11 | 12 | 10.5 | 45.5 |
| 11.5 | 12.5 | 11 | 46 |
| 12 | 13 | 11.5 | 47 |
| 13 | 14 | 12.5 | 48 |
Common Sizing Mistakes
- Buying UB 20 in your AF1 size. AF1 runs about half a size smaller in number than Ultraboost 20. If you wear AF1 in 10, take UB 20 in 10.5.
- Assuming UB 20 is narrower than earlier Ultraboosts. The Primeknit+ is denser but the last is the same — same width profile as 1.0 through 4.0. Wide feet still need half up.
- Carrying your Chuck Taylor size over. Chuck Taylor Ox runs about half a size smaller in number than UB 20. If you wear Chuck in 10, take UB 20 in 10.5.
- Expecting the heel frame to soften. The thermoplastic heel frame doesn't flex like a soft heel counter. If it feels too tight at the back, the issue is the frame geometry — not size. Ultraboost 21's redesigned frame may fit better.
- Confusing UB 20 and UB 4.0 sizing. They're the same — all Ultraboost generations (1.0–21) round to the same size in 0.5 increments. No adjustment needed between generations.
How Feetlot Computes These Numbers
Every Ultraboost 20 sizing recommendation on Feetlot is the output of a global offset model fit to over 100,000 owner-reported shoe records. Each shoe gets a single number — its "size offset" — that captures how its sizing drifts relative to a reference shoe (the Nike Air Force 1). When a Feetlot user provides their size in any tracked shoe, the model recovers their true foot baseline and recommends the matching Ultraboost 20 size.
This works better than the pairwise approach you'll see on most sizing blogs because Feetlot uses the entire wardrobe graph. A YEEZY 350 owner contributes data about how YEEZY fits relative to AF1 owners (who often own both), which links back to Ultraboost 20 owners through any shared model. Even when two users share zero shoes directly, the chain of users in between transmits a consistent recommendation.