Bike Frame Size Calculator
Seven free sizing modes for road, mountain, hybrid and gravel bikes: frame size from inseam, the LeMond saddle height method, reach & stack, standover clearance, a kids bike sizer, a size converter and a fit troubleshooter. Runs 100% in your browser.
Private — no data leaves your deviceFrame size from inseam & height
Measure inseam barefoot: stand against a wall, press a book firmly up into your crotch, measure floor to book top.
LeMond saddle height
The classic LeMond method: saddle height = inseam × 0.883, measured from the center of the bottom bracket to the top of the saddle along the seat tube.
Reach & stack explainer + stem adjuster
Copy frame reach and stack (mm) from the manufacturer geometry chart, then play with stem length, stem angle and spacers.
Standover clearance checker
Standover height is the top-tube height at its midpoint. You need at least 1 in (2.5 cm) of clearance on a road or hybrid bike, 1.5 in on gravel, and 2 in (5 cm) on a mountain bike.
Kids bike sizer
This kids bike size calculator sizes by wheel diameter, not frame size. Height is the primary measure — age is only a sanity check.
Bike size converter
Convert frame size between cm and inches, with an approximate brand letter (S/M/L/XL).
Fit troubleshooter
Pick your symptom — the tool maps it to the likely sizing cause and the direction of the fix.
How bike frame size is calculated
A bicycle frame size calculator turns your bike frame size by inseam into a starting frame size with one multiplication per discipline. The classic formulas used by this road bike frame size calculator, mountain bike frame size calculator and mtb frame size calculator are:
| Discipline | Formula | Example: 80 cm inseam |
|---|---|---|
| Road | inseam(cm) × 0.67 | 80 × 0.67 = 53.6 cm → 54 cm frame |
| Gravel | inseam(cm) × 0.67 − 1 | 53.6 − 1 = 52.6 cm → 52 cm frame |
| Hybrid (city) | inseam(cm) × 0.68 | 80 × 0.68 = 54.4 cm → 54 cm frame |
| Mountain (MTB) | inseam(cm) × 0.225 → inches | 80 × 0.225 = 18.0 in → 18 in frame |
Your hybrid bike frame size and gravel bike frame size land near the road number because the riding position is similar; gravel goes one size smaller for extra control off-road, and MTB frames are measured in inches with much lower standover. Rounding goes to the nearest commercial size (even cm numbers for drop-bar bikes, whole inches for MTB).
Bike frame size chart (Trek Madone geometry)
Formulas give a starting point; the brand chart decides. This bike frame size chart uses Trek Madone geometry (2022–2023 model years): compare your bike frame size by height and inseam against the row that fits.
| Frame (cm) | Rider height (cm) | Inseam (cm) | Stack (mm) | Reach (mm) | Standover (mm) |
|---|---|---|---|---|---|
| 52 | 163–168 | 75.9–79 | 561 | 371 | 732 |
| 54 | 168–174 | 78–82 | 575 | 374 | 744 |
| 56 | 174–180 | 81–85 | 591 | 377 | 768 |
A rider who is 174 cm tall with an 80 cm inseam sits on the 54: the formula says 53.6 cm and the chart puts 78–82 cm inseams on the 54. Cross-checking formula against chart is exactly what Mode 1 + Mode 3 do together.
Stack and reach explained
Bike reach and stack describe the frame better than seat-tube length ever could. Stack is the vertical distance from the bottom bracket to the top of the head tube; reach is the horizontal distance between the same two points. Stack and reach explained in one line: together they fix where your handlebars sit relative to your saddle, which is what your body actually feels.
Example from the chart above: a 54 cm Madone has 575 mm stack and 374 mm reach. Add a 90 mm stem at 6° and 20 mm of spacers and you get 463.5 mm of effective cockpit reach and a bar height of 604.4 mm above the bottom bracket. The stack/reach ratio is 1.54 — at or above 1.5 reads upright/endurance, below 1.4 reads aggressive/race. Mode 3 lets you test stem swaps before buying one: +10 mm of stem adds about 10 mm of reach.
Standover height and clearance
The standover height calculator (Mode 4) subtracts the bike standover height from your inseam. Standover clearance is a safety check, not a fit check: road and hybrid bikes need at least 1 in (2.5 cm), gravel 1.5 in (3.8 cm), and mountain bikes 2 in (5 cm) so you can bail out on technical terrain. Example: an 80 cm inseam over a 74.4 cm standover leaves 5.6 cm (2.2 in) of clearance — a PASS for road.
Kids bike size chart
Children are sized by wheel, not frame. This kids bike size chart follows height first — a child bike wheel size that lets both feet touch the ground is the safe one:
| Wheel | Child height (cm) | Typical age |
|---|---|---|
| 12 in | 76–100 | 2–3 |
| 14 in | 94–113 | 3–4 |
| 16 in | 100–123 | 4–6 |
| 20 in | 113–138 | 5–9 |
| 24 in | 132–153 | 8–12 |
| 26 in | 145–165 | 10+ |
A 120 cm tall 6-year-old lands on 20 in wheels (band 113–138 cm, typical age 5–9). Between bands, the smaller wheel is the safer first bike.
Size converter: cm, inches and S/M/L
The bike size converter (Mode 6) handles cm to inch bike frame math both ways: divide cm by 2.54, or multiply inches by 2.54. A 54 cm road frame is 21.3 in; an 18 in MTB frame is 45.7 cm. Brand letters are approximate: road XS below 50 cm, S 50–53, M 54–56, L 58–60, XL 62+; MTB XS ≤14 in, S ≤16, M ≤18, L ≤20, XL 21+. So 54 cm ≈ M and 18 in ≈ M — which is why bike frame size s/m/l labels alone are never enough; always check stack and reach too.
Saddle height: the LeMond method
This bike saddle height calculator (Mode 2) implements the LeMond method: the LeMond saddle height formula multiplies your inseam by 0.883 and measures from the center of the bottom bracket to the top of the saddle, along the seat tube. An 80 cm inseam gives 70.6 cm (706 mm). The formula was developed on 175 mm cranks, so the tool adjusts ±2.5 mm for every 5 mm of crank length difference, and can subtract 4 mm for modern clipless pedal stack. Any saddle height calculator is a starting point — fine-tune ±3 mm after riding.
Fit troubleshooter
The bike fit troubleshooter (Mode 7) maps symptoms to sizing causes. The classic knee pain bike fit rule: pain at the front of the knee usually means the saddle is too low (raise 3–5 mm toward your LeMond height); pain behind the knee usually means it is too high. Hips rocking side to side also point to a saddle set too high. Lower-back ache points to reach that is too long or bars that are too low — a shorter stem or more spacers first, a smaller frame if the gap is big. Toes hitting the front wheel (toe overlap) means the frame is too small.
Bike frame size FAQs
What size bike do I need for my height and inseam?
Take a rider who is 174 cm (68.5 in) tall with an 80 cm (31.5 in) inseam. Road: 80 x 0.67 = 53.6 cm, which rounds to a 54 cm frame (M). Mountain: 80 x 0.225 = 18.0 in, which rounds to an 18 in frame (M). Hybrid: 80 x 0.68 = 54.4 cm, which rounds to 54 cm. Gravel: 53.6 - 1 = 52.6 cm, which rounds to 52 cm. Then cross-check the brand chart — an 80 cm inseam sits on the 54 row of the Trek Madone chart above.
How does the LeMond saddle height formula work?
Measure your inseam barefoot with the book method, then multiply by 0.883. An 80 cm inseam gives 80 x 0.883 = 70.6 cm (706 mm). That is the distance from the center of the bottom bracket to the top of the saddle, measured along the seat tube. It is a starting point: fine-tune by a few millimeters after riding.
What do stack and reach mean on a geometry chart?
Stack is the vertical distance from the bottom bracket to the top of the head tube; reach is the horizontal distance between the same two points. A 54 cm Trek Madone lists 575 mm of stack and 374 mm of reach. With a 90 mm stem at 6 degrees and 20 mm of spacers, the effective cockpit reach is 463.5 mm and the bar height is 604.4 mm above the bottom bracket — a stack/reach ratio of 1.5, which reads upright and endurance-oriented.
How much standover clearance do I need?
At least 1 in (2.5 cm) on road and hybrid bikes, 1.5 in (3.8 cm) on gravel, and 2 in (5 cm) on mountain bikes. Example: an 80 cm inseam over a bike with 74.4 cm of standover leaves 5.6 cm (2.2 in) of clearance, which is a PASS for a road bike.
What wheel size bike does my child need?
Go by height, not age. A 120 cm tall 6-year-old fits 20 in wheels (the 113-138 cm band, typical age 5-9). A 100 cm 4-year-old fits 14 in wheels, and a 150 cm 11-year-old fits 26 in wheels. Between bands, pick the smaller wheel for a first bike.
How do I convert bike frame size from cm to inches?
Divide centimeters by 2.54: a 54 cm road frame is 21.3 in, roughly an M. Multiply inches by 2.54 to go the other way: an 18 in MTB frame is 45.7 cm, roughly an M in mountain sizing. Brand letters vary, so always confirm with stack and reach.
What should I do if I fall between two frame sizes?
Take the formula result of 53.6 cm, which sits between 52 and 54. Choose the smaller frame (52) for an aggressive, racy position or the larger (54) for endurance comfort and a taller head tube. It is easier to make a slightly small frame fit with a longer stem than to shrink a frame that is too big.
My front knee hurts — is my saddle too low?
Usually, yes. Pain at the front of the knee is the classic sign of a saddle set too low. Raise it 3-5 mm at a time toward your LeMond height — 70.6 cm for an 80 cm inseam — until the pain eases. Pain behind the knee means the opposite: the saddle is too high.
How do I measure my inseam correctly for bike sizing?
Stand barefoot against a wall with your feet about 20 cm apart. Press a hardcover book firmly up into your crotch, as if it were a saddle. Mark the wall at the top of the book and measure from the floor to the mark. Repeat two or three times and use the average — cycling inseam runs a little longer than trouser inseam.
Does crank length change the LeMond saddle height?
The 0.883 formula was developed on 175 mm cranks. For every 5 mm your cranks differ, move the saddle about 2.5 mm the other way: shorter cranks mean a slightly higher saddle, longer cranks a slightly lower one. Modern clipless pedals with thin soles also justify starting about 4 mm lower than the raw formula.
Free tool by NRTechStudio