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FIT LAB · FIT FINDERTell us age, height, and where your child wants to ride. Fit Lab gives you one parent-friendly fit report: starting size range, riding path, and what to check next.
These are starting recommendations, not a final fit. Final sizing should be checked in person.
Starting-point tables by sizing system. Each system is separate — numbers do not swap between tables. Balance / kids BMX / BMX Racing use XKids calibration; Freestyle and MTB are public-reference pending XKids calibration.
⚠Starter BMX, BMX Racing, Freestyle BMX, and MTB are separate sizing systems. A Junior race bike is not a Junior MTB; a 20" freestyle is not a 20" kids bike.
XKids calibration: from 85 cm. Inseam is the master measurement — seat at lowest should be about 1 inch below inseam.
| Wheel | Height | Inseam | Age |
|---|---|---|---|
| 12" | 85–105 cm · 33–41 in | 28–46 cm · 11–18 in | 1.5–3 yrs |
| 14" | 95–115 cm · 37–45 in | 35–52 cm · 14–20 in | 2–4 yrs |
| 16" | 105–122 cm · 41–48 in | 42–58 cm · 17–23 in | 3–5 yrs |
XKids calibration for the 12/14/16/18 starter BMX progression. Above 135 cm the neighborhood rider is better served by a regular kids bike / youth MTB-style fit.
| Wheel | Height | System | Notes |
|---|---|---|---|
| 12" | 100–115 cm · 39–45 in | XKids starter BMX | First pedal bike |
| 14" | 110–125 cm · 43–49 in | XKids starter BMX | Bigger kids on first bike |
| 16" | 120–135 cm · 47–53 in | XKids starter BMX | Confident pedalers |
| 18" | 135 cm+ · 53+ in | XKids starter BMX (cap) | Cascade to 24"+ for riders much above 135 cm |
| 20" | ~135–148 cm | Regular kids bike | Neighborhood cascade |
| 24" | ~135–155 cm | Regular kids bike / youth MTB | Neighborhood cascade |
| 26" youth XS | 150 cm+ | Youth XS / adult XS | Coach check required |
XKids calibration: Nano–Expert (90–150 cm). Above 150 cm is public-reference only and always needs a coach fitting before buying. Race classes are by top-tube length, not by rider age.
| Class | Top tube | Rider height | System |
|---|---|---|---|
| Nano | 15.5–16" | 90–105 cm · 2'11"–3'5" | XKids calibration |
| Micro | 16.25" | 105–115 cm · 3'5"–3'9" | XKids calibration |
| Mini | 17.25–17.5" | 115–125 cm · 3'9"–4'1" | XKids calibration |
| Junior | 18.25–18.75" | 125–140 cm · 4'1"–4'7" | XKids calibration |
| Expert | 19.5–20.0" | 140–150 cm · 4'7"–4'11" | XKids calibration |
| Expert XL | 20.0–20.25" | 150–168 cm · 4'11"–5'6" | Above XKids calibration — coach check |
| Pro | 20.5" | 157–173 cm · 5'2"–5'8" | Above XKids calibration — coach check |
| Pro L | 20.75–21.0" | 168–178 cm · 5'6"–5'10" | Above XKids calibration — coach check |
| Pro XL | 21.25" | 175–183 cm · 5'9"–6'0" | Above XKids calibration — coach check |
| Pro XXL | 21.5–21.75" | 180–200 cm · 5'11"–6'7" | Above XKids calibration — coach check |
20" wheel is standard from ~145 cm. Smaller riders use 14"/16"/18" kids freestyle frames. Between sizes, pick the shorter top tube. Currently using public references — XKids calibration is in progress.
| Bike | Top tube | Rider height |
|---|---|---|
| 14" kids freestyle | ~13" | 95–126 cm · 3'1"–4'2" |
| 16" kids freestyle | ~15" | 126–138 cm · 4'2"–4'6" |
| 18" kids freestyle | ~17" | 138–149 cm · 4'6"–4'10" |
| 20" short TT | 19.5–20.25" | 145–168 cm · 4'9"–5'6" |
| 20" mid TT | 20.25–20.75" | 160–178 cm · 5'3"–5'10" |
| 20" long TT | 21.0"+ | 175+ cm · 5'9"+ |
Wheel size plus standover. Kids MTB frames are deeper than BMX — confirm the child can plant a foot safely. Currently using public references — XKids calibration is in progress.
| Wheel | Height | Inseam | Typical terrain |
|---|---|---|---|
| 12" | 86–102 cm · 34–40 in | 38–46 cm · 15–18 in | First rides |
| 16" | 104–122 cm · 41–48 in | 41–56 cm · 16–22 in | Green trails |
| 20" | 114–137 cm · 45–54 in | 48–64 cm · 19–25 in | Green–blue trails |
| 24" | 124–150 cm · 49–59 in | 58–71 cm · 23–28 in | Blue trails |
| 26" youth XS | 142+ cm · 56+ in | 63+ cm · 25+ in | Blue–black trails |
Short answers to the questions we hear most. If your child is between sizes or you're not sure, send us their height and we'll help.
Height first, then riding style. For starter BMX / neighborhood riding: 12" at 100–115 cm, 14" at 110–125 cm, 16" at 120–135 cm, 18" at 135 cm+. BMX Racing uses different classes (Nano–Expert). Tell us height + riding style and we'll pick.
Inseam is the gate, not age. A balance bike from ~85 cm (seat ~1 inch below inseam). Move to a starter BMX / pedal bike when inseam is ~40 cm and the child can glide feet-up.
There's an overlap band (110–115 cm). Brand-new rider → 12". Confident pedaler at 110 cm → 14". When in doubt, size down for first bikes — control beats room-to-grow.
16" covers 120–135 cm. At 135 cm+ move to 18". If your child is well above 135 cm and just rides around the neighborhood, a regular 24" kids bike is often a better fit than staying on an 18" starter BMX.
Yes — that's the Micro class in XKids calibration (105–115 cm). Always start with a coach fitting on a real gate before buying a race frame.
Starter BMX (12/14/16/18) is a beginner kids bike. BMX Racing frames have gate-ready geometry and are sized by class (Nano / Micro / Mini / Junior / Expert) by top-tube length. The sizing tables don't swap.
Different sizing systems. Kids MTB goes by wheel size + standover. Freestyle BMX goes by height + top tube. Never use race classes for freestyle or MTB.
Height gives the race-class starting point. BMX Racing fit is more sensitive than normal kids-bike sizing — inseam, crank length, cockpit width, arm length, and track use can change the final setup. That's why we treat Racing recommendations as a starting class, not a final purchase decision.
Technical terms we use on this page, in one line each.
Starter BMX (12/14/16/18) and BMX Racing (Nano/Micro/Mini/Junior/Expert) use XKids internal calibration. Balance is XKids calibrated with an 85 cm floor. Above the XKids race range (>150 cm) and for Freestyle / MTB we currently use public references from Trek, Two Wheeling Tots, Rascal Rides, Supercross BMX, SkatePro, and Early Rider, with XKids coaching review on top. Numbers are starting points; real fit is confirmed in person.