Under Armour Boys' Size Chart
Complete boys' sizing guide for Under Armour with measurements, fit tips, and conversions
Use this boys size chart to compare your measurements against Under Armour's official sizing. Each table shows body measurements and international conversions.
Fit Notes
Under Armour publishes three explicit fit names — Compression, Fitted, and Loose — and the difference between them is much larger than most brands' equivalents, which makes reading the fit label more important than reading the size. Compression is genuinely skin-tight and drafted that way for performance; Loose is closer to what most competitors call regular fit, and Fitted sits in between. Footwear runs true in length but slightly narrow through the midfoot, especially on the HOVR line, and the Curry basketball models fit half a size long. Youth apparel uses the same three fit names but is drafted for a leaner block, so a Youth Loose is roughly an adult Fitted at the same chest.
How Under Armour Compares
Against Nike, Under Armour's Fitted tops sit close to a Nike Slim, and UA's Loose is closer to a Nike standard fit — cross-shoppers should map by fit name, not by numeric size. Against Adidas Techfit, UA Compression is comparable in tightness but longer in the body. Against Lululemon men's, UA Compression is more restrictive but less breathable at the same size.
Common Sizing Mistakes
The recurring mistake is buying a Compression top in the buyer's regular T-shirt size — Compression is meant to fit tight and the size chart already accounts for that, so sizing up neutralizes the performance benefit that justified the price. On shoes, wide-footed buyers frequently size up to compensate for a narrow HOVR when a half-size up doesn't actually widen the last — it just adds unwanted length. A third pitfall is the ColdGear line, which runs a hair tighter than the equivalent HeatGear at the same size to hold thermal loft against the skin.
Size data referenced from Under Armour's size chart, last verified July 2026.
Last updated: Q3 2026 · Reviewed quarterly by JC, SizeHub editor
Kids' Sizing
Clothing — Children (4–7 Years)
| Size | Chest (in) |
|---|---|
| 0/3M | 15.4–16.9 |
| 3/6M | 16.9–18.1 |
| 6/9M | 18.1–18.5 |
| 12M | 18.5–18.9 |
| 18M | 18.9–20.1 |
| 24M | 20.1–20.9 |
Shoes — Children (4–7 Years)
| US | UK | EU | CM |
|---|---|---|---|
| 1K | 0.5 | 16 | 7 |
| 4K | 3.5 | 19.5 | 10 |
| 7K | 6.5 | 23.5 | 13 |
| 10K | 9.5 | 27 | 16 |
| 11.5K | 11 | 28.5 | 17.5 |
| 13K | 12.5 | 31 | 19 |
| 1.5 | 1 | 33 | 20.5 |
| 3 | 2.5 | 35 | 22 |
| 4.5 | 4 | 36.5 | 23.5 |
| 6 | 5.5 | 38.5 | 24 |
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Frequently Asked Questions
Does Under Armour run small?
UA's Compression and Fitted lines may feel snug if you're used to relaxed-fit clothing. Their Loose fit is comparable to standard athletic brands.
What do UA fit types mean?
Compression: skin-tight for muscle support. Fitted: next-to-skin without squeezing. Loose: generous room for full mobility. Choose based on activity and preference.
How do UA shoes fit?
Under Armour shoes run true to US sizing. Their running shoes tend to be slightly narrow — consider half size up for wide feet.
How to Measure
Chest
Measure around the fullest part of your chest, keeping the tape horizontal.
Waist
Measure around your natural waistline, keeping the tape comfortably loose.
Hips
Stand with feet together and measure around the fullest part of your hips.