Get the wrong frame size, and even a $3,000 bike will feel uncomfortable. Get it right, and a $400 bike can ride for years without a single fit complaint. This free calculator covers road, mountain, hybrid, gravel, and kids’ bikes — using both the LeMond inseam method and height-based charts cross-referenced against Trek, Specialized, and Giant geometry data.
Enter your height (and inseam, if you have a measuring tape handy), and you’ll get a frame size recommendation tailored to your bike type and riding style. No sign-up required to use the tool. We’ve also included the full size charts, the inseam measurement guide, and the most common sizing mistakes people make — below the calculator.
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How This Bike Size Calculator Works
The calculator combines two trusted sizing methods so you get a range rather than a single number — which is how professional bike fitters actually work. A single number sounds precise, but bike geometry varies enough between brands that a “55 cm” Trek frame is not the same fit as a “55 cm” Cervelo frame.
For road, gravel, and hybrid bikes, the tool uses the LeMond inseam method: your cycling inseam in centimeters multiplied by 0.65 gives a starting frame size (center-to-top). We then cross-reference this against a height-based chart built from major manufacturer geometry tables (Trek Domane, Specialized Roubaix, Giant Defy, Cannondale Synapse) so the result accounts for proportional differences between people who share the same height.
For mountain bikes, sizing is dominated by reach (cockpit length) and standover clearance rather than seat tube length, so the tool returns the size letter (S/M/L/XL) that most brands use today, plus the approximate seat tube in inches for legacy reference. Kids’ bikes are sized by wheel diameter (12″, 16″, 20″, 24″, 26″), and inseam — not age — is the only number that matters.
Bike Size Charts by Type
If you prefer to look up your size on a chart rather than use the calculator, here are the same data tables the tool uses internally. Find your height in the left column, read across.
Road, Hybrid, and Gravel Bike Size Chart (cm)
These frame sizes are measured center-to-top (seat tube length) which is how most road, gravel, and hybrid manufacturers still publish their geometry charts.
| Your Height | Inseam (cm) | Frame Size | Letter |
|---|---|---|---|
| 4’10” – 5’1″ (147–154 cm) | 67–72 | 47–48 cm | XS |
| 5’1″ – 5’4″ (155–162 cm) | 72–77 | 49–50 cm | S |
| 5’4″ – 5’7″ (163–170 cm) | 76–81 | 51–53 cm | S-M |
| 5’7″ – 5’10” (171–178 cm) | 80–85 | 54–55 cm | M |
| 5’10” – 6’1″ (179–185 cm) | 84–89 | 56–57 cm | M-L |
| 6’1″ – 6’3″ (186–191 cm) | 88–93 | 58–59 cm | L |
| 6’3″ – 6’6″ (192–198 cm) | 92–97 | 60–62 cm | XL |
| 6’6″+ (199 cm+) | 97+ | 63+ cm | XXL |
See our shortlist of the best road bikes in 2026 and the budget-friendly best road bikes under $1,000 — both organized by frame size.
Mountain Bike Size Chart (S/M/L/XL)
Mountain bikes are sized by reach and standover rather than seat tube length, and the size letter is what most current brands print on their geometry charts. Use the inches column only if you’re shopping for a legacy or budget MTB that still lists seat tube length.
| Your Height | Frame Size (Letter) | Seat Tube (legacy) |
|---|---|---|
| Under 5’3″ (under 160 cm) | XS | 13–14″ |
| 5’3″ – 5’7″ (160–170 cm) | S | 15–16″ |
| 5’7″ – 5’11” (171–180 cm) | M | 17–18″ |
| 5’11” – 6’2″ (181–188 cm) | L | 19–20″ |
| 6’2″ – 6’5″ (189–195 cm) | XL | 21–22″ |
| 6’5″+ (196 cm+) | XXL | 23″+ |
Browse our top mountain bike picks in 2026 — we list the exact reach and stack for each model so you can confirm fit before buying.
Kids’ Bike Size Chart (by Inseam)
Kids’ bikes are sized by wheel diameter, not by frame size. Inseam is the only reliable input — age and height give wildly different results because growth is not uniform.
| Child’s Inseam | Wheel Size | Typical Age |
|---|---|---|
| Under 16″ (40 cm) | 12″ wheels | 2–4 years |
| 16–20″ (41–50 cm) | 16″ wheels | 4–6 years |
| 20–24″ (51–60 cm) | 20″ wheels | 6–9 years |
| 24–28″ (61–70 cm) | 24″ wheels | 9–12 years |
| 28″+ (71 cm+) | 26″ wheels or XS adult | 12+ years |
For first bikes, see the best starter bikes for kids ages 3–4.
How to Measure Your Inseam (the Right Way)
Your cycling inseam is not the same as your pants inseam. Pants inseam is measured from crotch seam to ankle while you’re wearing the pants. Cycling inseam is measured against your sit bones with a hard book pressed up between your legs — simulating the pressure of a bike saddle.
- Stand against a wall in your socks (no shoes), feet about 6 inches apart, back flat against the wall.
- Place a hardcover book spine-up between your legs, and pull it firmly upward into your crotch — the same pressure a bike saddle creates. Don’t be shy: most people under-pull and end up with an inseam that’s 2–3 cm too low.
- Mark the wall at the top of the book (where the spine meets the wall).
- Measure from the mark to the floor in centimeters or inches.
- Repeat twice and take the largest number. Pull-up pressure is the biggest source of error.
A friend reading the mark is more accurate than craning your neck down. If you’re between numbers, round up — a saddle set 0.5 cm too high is fine; one that’s too low causes knee pain.
Frame Size Isn’t Enough: Reach and Stack Explained
Two riders with identical 55 cm frames can ride completely differently because seat tube length tells you almost nothing about cockpit fit. The two numbers that actually determine how a bike feels are reach (horizontal distance from the bottom bracket to the head tube top) and stack (vertical distance between the same two points).
Reach controls how stretched out you’ll be over the handlebars. Stack controls how upright you’ll sit. An endurance road bike (Trek Domane, Specialized Roubaix, Giant Defy) typically has 15–20 mm more stack than a race bike (Trek Madone, Specialized Tarmac, Giant TCR) in the same size — same height, totally different position.
Once the calculator gives you a frame size, the next step is to compare reach and stack between specific models. If you’re moving from a known bike that fits well, copy its reach and stack figures and look for the new bike within ±10 mm on reach and ±15 mm on stack. That’s a much better predictor of comfort than the size letter on the sticker.
5 Common Bike Sizing Mistakes
Most bad bike purchases come from one of these five mistakes — not from trusting the wrong chart, but from skipping the verification step.
1. Buying by height alone for a road bike. Two riders at 178 cm can have a 6 cm inseam difference, which changes the right frame size by an entire step. Always pair height with inseam for drop-bar bikes.
2. Sizing up “to grow into it.” A bike that’s too big shortens the effective steering range, raises the standover (painful in emergencies), and pushes the handlebars too far away. For kids, this used to be standard advice and is now considered actively unsafe by most pediatric cycling resources. Size up for kids only if they have at least one season of riding behind them.
3. Trusting the e-commerce size chart over the manufacturer chart. Big retailers often simplify size charts to push more inventory. Always pull the geometry chart from the manufacturer’s product page (Trek, Specialized, Giant, Cannondale, etc.) before clicking buy.
4. Ignoring riding style. An aggressive race fit means lower stack and a longer reach — sizing down 1 cm gets you closer to that. An endurance or all-day-comfort fit means slightly higher stack and shorter reach — sizing up 1 cm gets you there. The same frame number is the wrong call for both riders.
5. Skipping the test ride for used bikes. Online used bikes often have non-stock stems, seatposts, or handlebars that alter the effective fit. The frame size on the seller’s listing is correct but the ride experience can be 2 sizes off. Always test ride or budget for a fit adjustment.
Bike Sizing FAQ
Is bike size measured in inches or centimeters?
Road, gravel, and hybrid bikes are almost always sized in centimeters (47 cm, 50 cm, 54 cm, etc.) measured center-to-top of the seat tube. Mountain bikes are sized in letters (XS/S/M/L/XL) on modern models and in inches (15″, 17″, 19″) on older or budget models. Kids’ bikes are sized by wheel diameter in inches (12″, 16″, 20″, 24″). Our calculator converts between all three.
What size bike for a 5’7″ (170 cm) person?
For a road, gravel, or hybrid bike, a 51–53 cm frame fits most people at 5’7″. For a mountain bike, a Small or low-end Medium frame. Inseam tilts the call: a 5’7″ rider with an 82 cm inseam should size up; with a 78 cm inseam, size down.
What size bike for a 6’0″ (183 cm) person?
A 56–57 cm road/gravel/hybrid frame fits most 6’0″ riders. For mountain bikes, a Large is standard. If you have a shorter torso and longer legs, lean toward 56 cm and check that the stack is comfortable.
Should I size up or size down if I’m between sizes?
For road and gravel bikes, the answer depends on your inseam-to-height ratio and your preferred riding position. Long inseam + endurance riding = size up. Short inseam + race riding = size down. For mountain bikes, the modern wisdom is to size up if you ride trail or enduro (more stability), size down only if you ride pure cross-country or technical climbs.
Does bike size affect comfort more than the saddle?
Yes. A wrong frame size cannot be fixed with a new saddle, handlebar swap, or stem change — only masked. A correct frame size with a mediocre saddle can be fixed with a $40 saddle upgrade. Frame size is the foundation; everything else is adjustment.
How accurate are online bike size calculators?
A height-only calculator is accurate to about ±1 size. A height-plus-inseam calculator like ours is accurate to about ±0.5 size for most riders. For competitive fitting or if you have an unusual proportion (very long torso, short legs, or vice versa), a professional bike fit is still worth $150–300 — especially before you spend $2,000+ on a bike.
Can two people share a bike if they’re close in height?
Up to a 5 cm height difference works if both riders adjust saddle height, and as long as the smaller rider can stand over the top tube with at least 2 cm of clearance. Above that, fit compromises start hurting one of the two riders.
Is frame size the same as wheel size?
No — except for kids’ bikes. Adult road, gravel, and hybrid bikes use 700c wheels regardless of frame size. Mountain bikes today use 29″, 27.5″, or occasionally 26″ wheels independently of frame size, though XS mountain frames sometimes pair with 27.5″ wheels for clearance.
Sources and Methodology
Frame size ranges in this calculator are derived from published 2024–2026 geometry tables for Trek (Domane, Madone, Émonda, Fuel EX), Specialized (Roubaix, Tarmac, Allez, Stumpjumper), Giant (Defy, TCR, Trance), Cannondale (Synapse, Topstone), Canyon (Endurace, Aeroad), and Cube (Attain, Reaction). The LeMond inseam method (inseam × 0.65) is documented in Greg LeMond’s Complete Book of Bicycling (1990) and remains the most commonly cited starting point for road bike fit. Kids’ wheel-size-by-inseam ranges follow guidance from REI Co-op Cycles and the Two Wheeling Tots research.
This calculator is intended as a starting point. For competitive cycling, time-trial, triathlon, or post-injury fitting, book a professional fit with a Retül-, BodyGeometry-, or Trek Precision-certified fitter.
Last updated: May 2026. We re-check this page against current manufacturer geometry charts twice a year.