How to size a Giant mountain bike
Giant keeps its mountain sizing simple with S, M, L and XL across most models (a few hardtails add XS or XXL), and it sizes by rider height and reach rather than seat tube. The one thing to watch is that Giant's reach steps can be large between sizes, and on the Reign in particular the jump from Medium to Large lands right where a lot of average height riders sit, so that model deserves a careful look. Flip chips and headset cups on most full suspension bikes let you fine tune reach and angle after you buy.
Have a look around: all Giant bikes at Bikeroom. Giant's women's specific range is sold under the Liv brand and is not covered here.
Before the numbers. These sizes are a considered starting point, not a rule. On a mountain bike your reach preference and riding style shift the answer, and Giant's height bands overlap so you can choose by feel. A test ride or fit is the final word.
Your Giant size by height
Find your height for the baseline size, which holds across the range; the model tables then give the reach so you can decide between two sizes.
| Rider height | Giant MTB size |
|---|---|
| 152 to 163 cm | XS (Stance and some hardtails) |
| 163 to 173 cm | S |
| 170 to 180 cm | M |
| 178 to 188 cm | L |
| 188 to 198 cm | XL |
The 170 to 180 cm band is where the Medium and Large overlap on most models. On the Reign, that overlap is the key decision, so read its note below.
How to choose your size
Start with height, measured barefoot. Then use reach to decide between sizes: compare the numbers below with a bike that already fits you well. On hardtails especially, do not be tempted to size up on standover alone, because Giant's sloping top tubes give deceptively generous clearance; size by reach instead. Remember the flip chip and headset options give a few millimetres of reach and about half a degree of angle either way.
The current MTB range, model by model
Anthem (XC)
The Anthem is the roomy, low slung XC racer. Its cockpit runs a touch long, so a rider wanting quicker handling can size down or fit a shorter stem.
| Frame size | S | M | L | XL |
|---|---|---|---|---|
| Reach (mm) | 415 | 440 | 460 | 485 |
| Rider height | 163 to 173 | 170 to 180 | 178 to 188 | 188 to 198 |
Trance and Trance X (trail)
The Trance is Giant's do it all trail bike, with the longer travel Trance X for rowdier riding. Both run long and stable, so if you want agility or a more upright feel, err to the smaller size. Reach below is the Trance X in its longer setting.
| Frame size | S | M | L | XL |
|---|---|---|---|---|
| Reach (mm) | 434 | 464 | 494 | 519 |
| Rider height | 163 to 172 | 171 to 180 | 179 to 188 | 187 to 196 |
Reign (enduro)
The Reign is the slack, hard charging enduro bike, and it is the model to size most carefully. The reach jumps 30 mm from Medium to Large right where many riders around 175 to 182 cm sit, so if you are in that band, compare both sizes closely or demo them.
| Frame size | S | M | L | XL |
|---|---|---|---|---|
| Reach (mm) | 430 | 460 | 480 | 510 |
| Rider height | 163 to 173 | 170 to 180 | 178 to 188 | 188 to 198 |
Fathom (trail hardtail)
The Fathom is the capable trail hardtail. Choose by reach and riding style, not standover, since a Medium and Large both suit many riders around 178 cm. The 27.5 and 29 versions share geometry.
| Frame size | S | M | L | XL |
|---|---|---|---|---|
| Reach (mm) | 425 | 445 | 470 | 490 |
| Rider height | 163 to 173 | 170 to 180 | 178 to 188 | 188 to 198 |
Stance (value full suspension trail)
The Stance is the accessible full suspension trail bike, now longer and more capable than before, and the only model here with an XS. It takes long dropper posts, which helps taller riders.
| Frame size | XS | S | M | L | XL |
|---|---|---|---|---|---|
| Reach (mm) | 407 | 422 | 454 | 477 | 509 |
| Rider height | 152 to 163 | 163 to 172 | 170 to 181 | 180 to 190 | 189 to 198 |
Trance X E+ and Reign E+ (e-MTB)
The Trance X E+ is the full power e-trail bike and the Reign E+ the full power e-enduro, both on Giant's own motor. They share the trail and enduro reach ladder, so size as you would the analogue bikes, with the same Medium to Large decision on the Reign E+.
| Frame size | S | M | L | XL |
|---|---|---|---|---|
| Reach (mm) | 430 | 460 | 480 | 510 |
| Rider height | 163 to 173 | 170 to 180 | 178 to 188 | 188 to 198 |
What Giant riders find
The single biggest talking point is the Reign's Medium to Large reach gap, which traps average height riders, so demo both if you are around 175 to 182 cm. More broadly the Trance, Trance X and Anthem run roomy in the cockpit, so riders wanting a livelier feel size down or shorten the stem. On hardtails like the Fathom and Talon, the generous standover tempts people to size up, but reach should decide. Owners of the Trance X E+ report it can feel a touch small, so some size up while others keep the Medium for standover and easy bailouts. The flip chips and headset cups across the full suspension range are a real tool for anyone sitting between sizes.
Between two sizes?
Smaller gives a nimble, playful ride, larger gives calm and stability. Use the reach numbers to break the tie, and on the Reign treat it as a genuine either or decision. Share your height and inside leg with us and we will talk it through.
Shop Giant MTB
- Giant Trance for trail
- Giant Stance for value full suspension
- All Giant bikes including the Anthem, Reign, Fathom and E+ e-MTBs
Weighing up a size? Ask our concierge
The Reign's size gap makes this a good one to talk through. Tell our concierge team your height, inside leg and the trails you ride, and we will recommend a size and model. Message our concierge.
These recommendations are general guidance, not a fitting guarantee. Reach figures reflect current Giant data and can change with flip chip settings and model years; some rider height ranges come from Giant's general chart rather than per model tables. Always confirm against the specific bike you are buying, ideally with a fit.
