Bike Sizes Guide
Bike size is your frame size in cm or inches, set by your inseam (road) or height (mountain). Quick rule: road frame ≈ inseam × 0.67; mountain frame ≈ inseam × 0.66 in inches. Full chart and calculator below.
Bike Size Calculator
Enter your measurements to find your recommended bike frame size.
How to Measure Your Inseam
- Stand barefoot against a wall with feet shoulder-width apart
- Place a book between your legs, spine up, pressing firmly against your crotch (simulating a bike seat)
- Mark the top of the book on the wall
- Measure from the floor to the mark - this is your inseam
- For most accurate results, have someone help you measure
Road Bike Frame Sizes
Road bikes are typically measured in centimeters and feature a more aggressive, aerodynamic riding position. Frame size directly affects your comfort and performance.
| Rider Height | Inseam Length | Frame Size (cm) | Frame Size (inches) | Size Label |
|---|---|---|---|---|
| 4'10" - 5'0" (147-152 cm) | 25" - 27" (63-68 cm) | 47-48 cm | 18.5" | XXS |
| 5'0" - 5'3" (152-160 cm) | 27" - 29" (68-73 cm) | 49-50 cm | 19.5" | XS |
| 5'3" - 5'6" (160-168 cm) | 29" - 31" (73-78 cm) | 51-52 cm | 20.5" | S |
| 5'6" - 5'9" (168-175 cm) | 31" - 33" (78-83 cm) | 53-54 cm | 21.5" | M |
| 5'9" - 6'0" (175-183 cm) | 33" - 35" (83-88 cm) | 55-56 cm | 22.5" | L |
| 6'0" - 6'3" (183-191 cm) | 35" - 37" (88-93 cm) | 57-58 cm | 23.5" | XL |
| 6'3" - 6'6" (191-198 cm) | 37" - 39" (93-99 cm) | 59-60 cm | 24.5" | XXL |
Mountain Bike Frame Sizes
Mountain bikes are usually sized in inches or with S/M/L labels. They feature a more upright position than road bikes and are designed for off-road terrain.
| Rider Height | Inseam Length | Frame Size (inches) | Size Label |
|---|---|---|---|
| 4'10" - 5'2" (147-157 cm) | 25" - 27" (63-68 cm) | 13" - 14" | XS |
| 5'2" - 5'6" (157-168 cm) | 27" - 29" (68-73 cm) | 15" - 16" | S |
| 5'6" - 5'10" (168-178 cm) | 29" - 31" (73-78 cm) | 17" - 18" | M |
| 5'10" - 6'1" (178-185 cm) | 31" - 33" (78-83 cm) | 19" - 20" | L |
| 6'1" - 6'4" (185-193 cm) | 33" - 35" (83-88 cm) | 21" - 22" | XL |
| 6'4"+ (193+ cm) | 35"+ (88+ cm) | 23"+ | XXL |
Kids Bike Sizes
Kids bikes are sized by wheel diameter rather than frame size. Choose based on the child's height and age for the best fit and safety.
| Child's Height | Age Range | Inseam | Wheel Size |
|---|---|---|---|
| 2'10" - 3'4" (85-100 cm) | 2-4 years | 14" - 17" (35-43 cm) | 12" |
| 3'4" - 3'8" (100-110 cm) | 4-5 years | 16" - 20" (40-50 cm) | 14" |
| 3'8" - 4'0" (110-120 cm) | 5-7 years | 18" - 22" (45-55 cm) | 16" |
| 4'0" - 4'5" (120-135 cm) | 7-9 years | 22" - 25" (55-63 cm) | 20" |
| 4'5" - 4'9" (135-145 cm) | 9-11 years | 24" - 28" (60-70 cm) | 24" |
| 4'9"+ (145+ cm) | 11+ years | 26"+ (66+ cm) | 26" or Adult |
BMX Bike Sizes
BMX bikes are primarily sized by top tube length and wheel size. Most adult BMX bikes use 20" wheels, while younger riders may need 18" or smaller.
| Rider Height | Age Range | Top Tube Length | Wheel Size |
|---|---|---|---|
| 3'0" - 3'8" (90-110 cm) | 3-6 years | 14" - 16" | 12" - 14" |
| 3'8" - 4'4" (110-130 cm) | 6-9 years | 16" - 18" | 16" - 18" |
| 4'4" - 5'0" (130-152 cm) | 9-12 years | 18" - 19" | 18" - 20" |
| 5'0" - 5'4" (152-163 cm) | 12+ years | 19" - 20" | 20" |
| 5'4" - 5'8" (163-173 cm) | Adult | 20" - 20.5" | 20" |
| 5'8" - 6'0" (173-183 cm) | Adult | 20.5" - 21" | 20" |
| 6'0"+ (183+ cm) | Adult | 21" - 22" | 20" or 24" |
Hybrid & City Bike Sizes
Hybrid and city bikes offer a comfortable, upright riding position. They're typically sized similarly to mountain bikes but may use different labeling systems.
| Rider Height | Frame Size (inches) | Frame Size (cm) | Size Label |
|---|---|---|---|
| 4'10" - 5'2" (147-157 cm) | 13" - 14" | 33 - 36 cm | XS |
| 5'2" - 5'6" (157-168 cm) | 15" - 16" | 38 - 41 cm | S |
| 5'6" - 5'10" (168-178 cm) | 17" - 18" | 43 - 46 cm | M |
| 5'10" - 6'1" (178-185 cm) | 19" - 20" | 48 - 51 cm | L |
| 6'1" - 6'4" (185-193 cm) | 21" - 22" | 53 - 56 cm | XL |
| 6'4"+ (193+ cm) | 23"+ | 58+ cm | XXL |
Electric Bike (E-Bike) Sizes
E-bikes follow similar sizing to their non-electric counterparts. However, consider the added weight when choosing frame size and style. Step-through frames are popular for easier mounting/dismounting.
E-Bike Size Guidelines:
- Road E-Bikes: Follow road bike sizing chart
- Mountain E-Bikes: Follow mountain bike sizing chart (may size down slightly due to weight)
- City/Commuter E-Bikes: Follow hybrid bike sizing chart
- Cargo E-Bikes: Usually one-size-fits-most with adjustable components
- Folding E-Bikes: One-size-fits-most, typically suits riders 5'2" - 6'2"
Additional E-Bike Considerations:
- Battery placement affects center of gravity
- Heavier weight means more important to get correct frame size
- Step-through frames easier to mount with extra weight
- Adjustable stems and seat posts help fine-tune fit
Bike Fit Tips & Adjustments
Test Ride Checklist:
- Stand-over height: Should have 1-2 inches clearance (road) or 2-4 inches (mountain) when standing over top tube
- Reach: When seated, elbows should be slightly bent when holding handlebars
- Knee position: At bottom of pedal stroke, knee should have slight bend (25-30 degrees)
- Back comfort: Shouldn't feel overstretched or cramped
- Handlebar height: Should allow comfortable posture without strain
Fine-Tuning Your Fit:
- Saddle height: Most critical adjustment - affects power and comfort
- Saddle fore/aft: Knee should be above pedal axle when crank is horizontal
- Saddle tilt: Start level, adjust slightly nose-down if uncomfortable
- Handlebar height: Raise for comfort, lower for aerodynamics
- Stem length: Can be changed to adjust reach
When to Size Up or Down:
- Size up if: Between sizes and prioritize comfort, have long legs/short torso, plan long rides
- Size down if: Between sizes and prioritize maneuverability, have short legs/long torso, ride aggressively
- Road bikes: Err on smaller side for racing, larger for comfort
- Mountain bikes: Smaller frame offers more control on technical terrain
Understanding Frame Geometry
Key Measurements:
- Seat Tube Length: Traditional frame size measurement, from bottom bracket to top of seat tube
- Top Tube Length: Affects reach - longer tube = more stretched position
- Head Tube Angle: Steeper (73-75°) = quick handling; Slack (66-68°) = stable at speed
- Seat Tube Angle: Affects pedaling position - steeper = more forward, better for climbing
- Wheelbase: Distance between axles - longer = more stable, shorter = more nimble
- Bottom Bracket Drop: Lower = more stable, higher = better clearance
- Reach & Stack: Modern sizing metrics measuring horizontal and vertical distance from BB to head tube