Bike Size Calculator
Measure from the floor to your crotch while standing straight. See the measurement guide below.
Optional — used for saddle height estimation if provided.
Enter Your Measurements
Select your bike type and enter your height or inseam length above to get your recommended frame size, size label, saddle height, and more.
How to Measure Your Inseam
- Remove your shoes and stand with your back flat against a wall.
- Place a hardcover book or similar object firmly between your legs at crotch height, with its spine facing up.
- Ask someone to measure the distance from the top edge of the book to the floor.
- Take two or three measurements and use the average for best accuracy.
How to Use the Bike Size Calculator
Select Your Bike Type
Choose the type of bike you are shopping for: Road, Mountain, City/Hybrid, BMX, or Kids. Each type uses different sizing conventions and formulas, so selecting the correct type is essential for accurate results.
Enter Your Measurements
For road, mountain, and city bikes, enter your inseam length for the most accurate result (see the measurement guide at the bottom of the page). You can also use height-only mode if you do not have your inseam handy. For BMX bikes, only height is needed. For kids' bikes, enter the child's height and age.
Choose Your Riding Style (Road Bikes)
If you selected Road as your bike type, choose your preferred riding style: Aggressive/Performance for a racy aerodynamic position, Endurance/All-Round for a balanced setup, or Casual/Comfort for an upright relaxed posture. This adjusts the frame size recommendation by up to 1 cm.
Review Your Results
Check your recommended frame size in both centimetres and inches, your size label (XS through XXL), optimal saddle height, crank length recommendation, and standover clearance guidance. If you fall between two sizes, the calculator will explain which direction to lean based on your riding style. Export your results as a CSV to take bike shopping.
Frequently Asked Questions
What is the most accurate way to measure inseam for bike sizing?
The most accurate method is to stand without shoes with your back against a wall, place a hardcover book firmly between your legs at crotch height (simulating a bike saddle), and have someone measure from the top of the book to the floor. Take two or three measurements and average them. This 'book method' is recommended by professional bike fitters because it mimics how a saddle supports your weight. Simply reading a trouser inseam from clothing is less accurate because garment inseams are cut shorter than actual body inseam for fitting purposes — always measure directly.
Should I use my height or inseam to size a bike?
Inseam is the more accurate measurement and should be your primary input whenever possible. Two riders of identical height can have very different inseam lengths due to differences in leg-to-torso proportions, and these riders would fit very differently on the same bike. Height-based sizing is a convenient approximation but can be off by one full size in some cases. The calculator provides a height-only mode for quick estimates, but for any significant bicycle purchase, measure your inseam using the book method and enter that figure for the most reliable recommendation.
What does it mean to be between sizes, and what should I do?
Being between sizes means your measurements fall within about 1.5 cm of a size boundary, where either of two adjacent sizes could work. The best approach depends on your riding style. Performance-oriented cyclists who want a more aerodynamic, responsive position typically do better on the smaller size, as it allows a lower reach without excessive stretching. Comfort or casual riders who prefer a more upright, relaxed posture often prefer the larger size. If possible, test ride both sizes before deciding. A longer stem can compensate for a slightly small frame; a shorter stem and a set-back seatpost can make a slightly large frame more manageable.
Why is the mountain bike frame size so much smaller than road bike size for the same rider?
Mountain bikes use a compressed size scale compared to road bikes because they require significantly more standover clearance — the gap between the rider's crotch and the bike's top tube when standing over it flat-footed. On a road bike, 1–2 cm of standover clearance is sufficient because you rarely need to put both feet down quickly. Mountain bikers frequently need to dismount suddenly during technical descents or obstacle sections, so 5–10 cm of clearance is recommended for safety. This extra clearance requirement means mountain bike seat tubes are proportionally shorter relative to the rider's inseam, which is why the multiplier (0.59) is lower than for road (0.67) or city (0.64) bikes.
How is saddle height different from frame size?
Frame size and saddle height are two separate, complementary measurements. Frame size (seat tube length) determines the overall dimensions of the bicycle and is fixed once you purchase a bike. Saddle height is an adjustable component — you can raise or lower the seat post to fine-tune your leg extension. This calculator recommends a saddle height using the LeMond method (Inseam × 0.883), which is the distance from the centre of the bottom bracket to the top of the saddle. Setting saddle height correctly is critical for efficient pedalling and knee health — too low causes knee pain at the front of the knee; too high causes pain at the back. Use the calculator's saddle height recommendation as your starting point and make small adjustments from there.
How do I choose the right wheel size for a kids' bike?
Kids' bikes are sized primarily by wheel diameter, which is more relevant than frame size for very young children. The general guide is: 12-inch wheels for ages 2–3 (under 90 cm tall), 14-inch for ages 3–4 (90–100 cm), 16-inch for ages 4–5 (100–110 cm), 20-inch for ages 5–8 (110–125 cm), 24-inch for ages 8–11 (125–145 cm), and 26-inch for 11 and older. Height is actually a more reliable indicator than age alone, since children develop at very different rates. The most important fitting criterion is that your child can place both feet flat (or nearly flat) on the ground while sitting on the saddle — this gives them confidence and control when stopping.