Bike Sizes Guide
Finding the right bike size is crucial for comfort, performance, and injury prevention. This comprehensive guide covers sizing for road bikes, mountain bikes, kids bikes, BMX, and more.
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