The best way to size your rider’s new bike is by Inside Leg measurement.

By all means supplement with height and age as a guide, but Inside Leg is more accurate as there is a large spread of leg lengths/heights for each age. This is easy and only takes a few seconds;

• Stand your rider in socks against a wall
• Put a small book between their legs (like a saddle, high as comfortable) and against the wall
• Ask your rider to move away, measure from the top of the book to the floor, using cm or inches.

We list Minimum Inside Leg our kids race bikes (full Geo listed below) on each product page. We measure from the floor up to the top-tube, in-front of the saddle, then minus 2-4cm for shoes, depending on age... 

HUP evo:

50cm: Seat Tube 50cm | VTT 52.3cm | Reach 37.3cm | Stack 53.4cm | HT 120mm | HT Angle 71 degrees
52cm: Seat Tube 52cm | VTT 53.8cm | Reach 37.7cm | Stack 54.5cm | HT 130mm | HT Angle 71.5 degrees
54cm: Seat Tube 54cm | VTT 55cm | Reach 38cm | Stack 55.7cm | HT 140mm | HT Angle 72 degrees
56cm: Seat Tube 56cm | VTT 56.2cm | Reach 38.9cm | Stack 56.5cm | HT 155mm | HT Angle 72 degrees
58cm: Seat Tube 58cm | VTT 57.4cm | Reach 39.5cm | Stack 58.4cm | HT 175mm | HT Angle 72 degrees
Standover (floor to top-tube, in front of saddle): 50cm: 74cm | 52cm: 77cm | 54cm: 80cm | 56cm: 82cm | 58cm: 84cm

HUP straatrace:

Kids Sizes*
37cm: Seat Tube 37cm | VTT 49.5cm | Reach 35.3cm | Stack 48.5cm | HT 90mm | HT Angle 70 degrees
44cm: Seat Tube 44cm | VTT 50.5cm | Reach 36.3cm | Stack 49.5cm | HT 100mm | HT Angle 70 degrees
48cm: Seat Tube 48cm | VTT 51.8cm | Reach 38cm | Stack 50.6cm | HT 105mm | HT Angle 72 degrees
Actual Standover (floor to top-tube, just in front of saddle nose): 37cm: 63cm | 44cm: 67cm | 48cm: 71cmSize Guide (height/inside leg): 37cm: 130cm+ (59-69cm) | 44cm: 138cm+ (64-77cm) | 48cm: 145cm+ (68-78cm)
Size Guide (height/inside leg): 37cm: 130cm+ (59-69cm) | 44cm: 138cm+ (64-77cm) | 48cm: 145cm+ (68-78cm)

HUP azure:

Kids Sizes*
37cm: Seat Tube 37cm | VTT 49.5cm | Reach 37.7cm | Stack 47.2cm | HT 90mm | HT Angle 71 degrees
44cm: Seat Tube 44cm | VTT 50.5cm | Reach 38.5cm | Stack 48cm | HT 100mm | HT Angle 71 degrees
48cm: Seat Tube 48cm | VTT 51.8cm | Reach 39.5cm | Stack 49cm | HT 105mm | HT Angle 72 degrees
Size Guide (height/inside leg): 37cm: 130cm+ (59-69cm) | 44cm: 138cm+ (64-77cm) | 48cm: 145cm+ (68-78cm)

Adult Sizes
50cm: Seat Tube 50cm | VTT 53.1cm | Reach 39.8cm | Stack 50.5cm | HT 110mm | HT Angle 73 degrees
52cm: Seat Tube 52cm | VTT 54.4cm | Reach 40.5cm | Stack 52cm | HT 120mm | HT Angle 75 degrees
Standover (floor to top-tube, in front of saddle): 37cm: 63cm | 44cm: 67cm | 48cm: 71cm | 50cm: 74cm | 52cm: 77cm

HUP enduro:

13": Seat Tube 33cm | VTT 52cm | Reach 36.3cm | Stack 58cm | STA 75 deg | HT 10cm | HTA 65 deg | Stays 445mm
15.5": Seat Tube 39.5cm | VTT 58cm | Reach 42cm | Stack 59cm | STA 75 deg | HT 10cm | HTA 65 deg | Stays 445mm
17.5": Seat Tube 44.5cm | VTT 61cm | Reach 45cm | Stack 60cm | STA 75 deg | HT 11cm | HTA 65 deg | Stays 445mm
Actual Standover (floor to top-tube, in front of saddle) on 27.5" wheels/100mm fork: 13": 59cm | 15.5": 66cm | 17.5: 69cm. Tip: If you size with the saddle slammed, they've no room to move, so (unlike Road/CX) it's better to size down.
Size Guide (height/inside leg): 13": 120cm+ (55-65cm) | 15.5": 145cm+ (62-72cm) | 17.5": 155cm+ (68cm+)
Dropper Fitment: If you require a dropper post, the riders Inside leg needs to be at least equal to Seat Tube Length + Crank Length + Dropper Travel + 100mm to use the full dropper travel, otherwise only some travel will be useable.

* For small adults using the kids sizes, get in touch to confirm the best fit for you

Component Sizing Guide

Drop Handlebars: match the approx shoulder width for Road, or shoulder width +1 size up for Cyclocross

Flat Handlebars: match the approx width of their press-up position (go narrower for XC, wider for Enduro)

Cranks: take 10% of their height +5mm for crank length (Road & Triathlon cycling) or 10% of their height +10mm for crank length (Off-Road cycling). Example: 1350mm tall rider would choose 140mm for Road bike or 145mm for CX/MTB.

Stems: This isn't an exact science, but generally if the rider is at the lower end of the frameset's growth range, a shorter stem will be correct and vice-versa.

Saddle/Post: Our kids saddle is suited to younger riders and the Youth saddle for older riders (or younger riders Off-Road). But saddles are a personal thing. We have 2 choices of seat post, inline or rotary, the later is very useful for smaller riders at the lower end of the frameset's growth range being reversible to reduce the bikes effective length.