Bike Sizing Chart: How to Choose the Right Bike Size

Riding a bike that fits right makes all the difference in comfort, efficiency, and control. Too big, you’ll struggle to handle it, and too small, you’ll feel cramped. The right fit will help you ride longer without discomfort and improve handling.

Before you buy a bike, ask yourself:

• What type of bike do I need? (Mountain, road, gravel, etc.)
• How tall am I? (Consider both height and inseam length.)
• What’s my riding style? (Aggressive or casual rider?)

A local bike shop can help dial in the perfect fit, but knowing the basics will give you a good starting point. We’ll walk you through everything you need to know about bike sizing, including key measurements, fit adjustments, and how different types of bikes affect sizing.

Why The Right Size Bike Matters

Riding a bike that fits well improves your experience in several ways:

• Control: The right frame size helps with stability and handling.
• Efficiency: A proper fit allows you to pedal more effectively and avoid wasted energy.
• Comfort: A well-sized bike reduces strain on your back, neck, and knees.

What to Look for in the Perfect Fit

A few simple checks set the foundation and help determine if a bike fits well:

• Knee bend: Your leg should have a slight bend at the bottom of the pedal stroke (about 25-35 degrees of flexion).
• Standover clearance: When standing over the top tube, you should have some clearance.
• Reach: Your upper body should feel comfortable reaching the handlebars without strain or feeling too stretched out.

How to Measure Yourself for a Bike Size

Getting the right fit starts with proper measurements.

#1. Height & Inseam

These are the two main factors for determining the right bike size.

• Height: Stand straight against a wall and measure from the floor to the top of your head.
• Inseam: Stand with your feet about 6 inches apart and measure from the floor to your crotch.

Use these numbers to compare with a bike size chart for your preferred type of bike.

#2. Standover Height

Standover height is the clearance between your body and the bike’s top tube when you straddle it.

• You should have at least 1 inch of clearance for road bikes.
• For mountain bikes, 2-3 inches is better.

Measure this by standing over the bike with your shoes flat on the ground and checking the gap.

#3. Stack

Stack is the vertical distance from the bottom bracket to the top of the head tube.

• Taller riders need more stack for an upright position.
• Aggressive riders often prefer a lower stack for aerodynamics.

You can measure this with a tape measure or check the manufacturer’s specs.

#4. Reach

Reach is the horizontal distance from the bottom bracket to the handlebars. Sit on the bike and check if you can comfortably reach the handlebars without feeling too cramped.

• Your arms should be slightly bent when holding the bars.
• If you feel too stretched out or cramped, adjustments to the stem or handlebars can help.

#5. Leg Extension

Your leg should extend almost fully when pedaling but should never lock out.

• Sit on the saddle and place your heel on the pedal at its lowest position.
• Your leg should be almost straight but not fully locked.
• If your knee is bent, the saddle is too low. If you overextend, it’s too high.

Should Your Feet Touch the Ground?

Not necessarily. When seated, your toes might barely touch the ground, but you shouldn’t be flat-footed. If you are, your saddle is likely too low.

Bike Size Considerations

#1. Seat Tube Length

This measurement determines the bike’s frame size and how low the saddle can be adjusted.

• Measured from the bottom bracket to the top of the seat tube.
• A longer seat tube raises the saddle height, while a shorter seat tube allows for a lower saddle position. 

#2. Top Tube Length

The top tube length affects how far you have to extend your arms to the handlebars.

• A longer top tube means a more stretched-out position.
• A shorter top tube keeps your posture more upright.

#3. Wheel Size

Front and rear wheel size affects how a bike handles, accelerates, and absorbs bumps.

• Road bikes typically use 700c wheels, which are fast and efficient on pavement.
• Mountain bikes have multiple sizes:
  • 26-inch wheels offering agility and an old school feel
  • 27.5-inch wheels balancing speed and maneuverability
  • 29-inch wheels rolling smoothly over rough terrain.
• Kids bikes and smaller adult bikes may use 24-inch wheels for a more proportional fit.

#4. Handlebar Width

Handlebar width should match your shoulder width for optimal control and comfort.

• Wider handlebars improve stability on mountain bikes.
• Narrower bars enhance aerodynamics on road bikes.

Mountain vs. Road Bike Sizes

Mountain Bikes

Mountain bikes are built for off-road terrain, so sizing affects both comfort and control. A properly sized mountain bike allows for better maneuverability, stability, and shock absorption when riding over rocks, roots, and uneven surfaces.

• Frames are generally sized xx-small all the way to xx-large in rare instances.  (e.g.,XS, S, M, L, XL). Always be sure to check the brand’s sizing chart, as sizes can vary, and the measurement numbers are the most important part of a frame size.
• Aim for 2-3 inches of clearance between you and the top tube when standing over the bike.
• A longer top tube and shorter stem improve stability.
• Most modern mountain bikes use 27.5” or 29” wheels. 
• Riders often size down for better control on technical terrain.

Road Bikes

Road and track bikes are designed for speed on pavement, making proper sizing essential for comfort and performance. A well-fitted road bike helps maintain an aerodynamic posture, reduces strain on long rides, and improves pedaling efficiency.

• Frames are typically measured in centimeters (e.g., 52cm, 54cm, 56cm). Check the manufacturer’s sizing chart.
• At least 1 inch of clearance over the top tube is ideal.
• A longer reach and lower stack promote a fast riding position.
• Almost all road bikes use 700c wheels
• Some riders prefer a more upright geometry for comfort on long rides.

What If You’re Between Bike Sizes?

If you fall between two bike sizes, choosing the right one often comes down to personal preference and riding style. Going to a professional bike fitter is always the best option to be sure you have the perfect size bike for your body type.

Size Up If:

• You want a more stable, stretched-out position (better for road biking).
• You have longer arms or legs and need extra reach.
• You ride long distances and prioritize efficiency.
• You can adjust the fit with a longer seat post, stem, or wider handlebars.

Size Down If:

• You want better maneuverability and control (better for mountain biking).
• You prefer quick handling, especially on technical trails.
• You have a shorter reach and want a more compact fit.
• You can adjust the fit with a shorter stem, lower saddle, or adjusted handlebar positioning.

Thomson Tip: Test Ride & Feel

If you’re looking to purchase a new bike, we recommend test riding both sizes to see which one feels more natural. If unsure, lean toward the smaller frame. It’s usually easier to adjust for fit and control than one that’s a larger size.

Thomson: Designed for Riders Who Demand More

A properly sized bike makes all the difference, but the right components take it to the next level. Thomson helps riders customize their fit for better comfort and control on every ride.

We offer customizable mountain, road, and gravel frames, allowing you to choose from different sizes to match your riding style and needs. Once you’ve found your ideal frame design, you can fine-tune your setup with stems, seatposts, handlebars, and more.