Short answer: height gives you a starting range, inseam narrows it, and neither settles it. Two riders at 175cm can genuinely need different frames because torso and arm length vary independently of height. Use the tables below to get within one size, then check the brand's own chart and, above a certain spend, get fitted.
Contents
- Start with height
- Refine with inseam
- Why frame size numbers stopped meaning much
- Stack and reach: what actually matters
- Caught between two sizes?
- Your brand's own chart
- What a chart cannot tell you
- FAQ
Start with height
This is a starting point, not an answer. Sizes vary between manufacturers by a full size in places.
Road bikes
| Rider height | Frame size | Label |
|---|---|---|
| 152 to 160cm | 47 to 49cm | XXS / XS |
| 160 to 168cm | 50 to 52cm | XS / S |
| 168 to 175cm | 53 to 54cm | S / M |
| 175 to 182cm | 55 to 56cm | M / L |
| 182 to 189cm | 57 to 58cm | L / XL |
| 189 to 196cm | 59 to 61cm | XL / XXL |
Gravel bikes
Most gravel frames follow road sizing closely, though usually badged S/M/L rather than in centimetres. If you know your road size, start there and expect the gravel equivalent to sit within one size.
Mountain bikes
| Rider height | Frame size |
|---|---|
| 155 to 165cm | XS / S |
| 165 to 175cm | S / M |
| 175 to 183cm | M / L |
| 183 to 191cm | L / XL |
| 191cm and above | XL / XXL |
Mountain bike sizing has moved almost entirely to reach rather than seat tube length, so a modern large can have a shorter seat tube than a ten-year-old medium. Height bands are a rougher guide here than on road.
Refine with inseam
Inseam is a better predictor than height because it separates leg length from torso length, the thing height alone hides.
How to measure it properly. Barefoot, heels about 15cm apart, back against a wall. Put a hardback book between your legs and pull it up firmly against your crotch, spine level. Have someone measure from the floor to the top edge of the book. Do it three times and take the middle number, because the variation between attempts is usually a centimetre or more and it matters.
Two rules of thumb, both approximate:
| Calculation | Gives you |
|---|---|
| Inseam (cm) x 0.65 | Approximate road seat tube length, centre to centre |
| Inseam (cm) x 0.883 | Approximate saddle height, from bottom bracket centre to saddle top |
The second is more useful in practice. Saddle height is what you actually set, and it carries across frames. Once you know yours, you can replicate it on any bike.
Why frame size numbers stopped meaning much
"56cm frame" used to describe a bike reliably, when top tubes were horizontal and seat tube length told you almost everything. That stopped being true for three reasons.
Sloping top tubes. Almost every modern frame slopes the top tube down towards the seat tube. This shortens the seat tube without changing how big the bike actually rides, so the number on the label no longer describes the fit.
Inconsistent measuring. Some manufacturers measure seat tube centre-to-centre, others centre-to-top. That difference alone is often 10 to 15mm, which is most of a size.
Labels are not standardised. One brand's medium is another's 54, and a third calls the same fit a large.
This is why comparing a 56cm from one brand against a 56cm from another tells you very little.
Stack and reach: what actually matters
Stack and reach were introduced precisely to solve the problem above. They describe the frame independently of how it is constructed or labelled.
| Measurement | What it is | What it controls |
|---|---|---|
| Stack | Vertical distance from bottom bracket centre to the top of the head tube | How upright the bike is |
| Reach | Horizontal distance from bottom bracket centre to the top of the head tube | How stretched out you are |
Because both are measured from the bottom bracket and ignore components entirely, they are directly comparable across any two frames from any two brands.
The ratio between them tells you the bike's intent. Around 1.4 is an aggressive race position. Above roughly 1.5 is endurance geometry, more upright and more comfortable over distance.
The practical use: if a bike currently fits you well, find its stack and reach in the manufacturer's geometry chart and write them down. That pair of numbers will identify your size on any other bike far more reliably than your height ever will.
Caught between two sizes?
Most riders land between sizes at some point. What decides it is which dimensions you can adjust afterwards and which you cannot.
| Adjustable after purchase | Fixed by the frame |
|---|---|
| Saddle height (seatpost) | Stack |
| Saddle fore/aft (rails, seatpost offset) | Reach |
| Reach to bars (stem length, plus or minus 20mm usefully) | Standover height |
| Bar height (spacers, stem angle) | Wheelbase and handling |
Size down if you want a more aggressive position, need more standover clearance, or have a shorter torso for your height. You can lengthen the stem to recover reach, up to around 120 to 130mm before steering starts to feel slow.
Size up if you want a more relaxed position, have a long torso, or the smaller size would need an unusually long stem. You can shorten the stem, though below about 70mm the steering gets twitchy.
The asymmetry worth knowing: a stem is a cheap part with real adjustment range. Standover clearance and stack are not adjustable at all. If the smaller size leaves you short on standover, that decides it.
Your brand's own chart
Once you are within one size, use the manufacturer's chart for the specific model. That is the only source with the actual geometry.
| Brand | Charts |
|---|---|
| Basso | Venta · Astra |
| Cannondale | Synapse · Topstone |
| Cervelo | Soloist · Caledonia |
| Felt | Road |
| Fuji | Endurance Road |
| Kona | Road · MTB |
| Look | Road |
| Merida | Road · Scultura · Gravel · Hybrid · MTB Hardtail · Crossway |
| Orbea | Road |
| Pardus | All models |
| Polygon | Road · Gravel |
| Specialized | Road |
A note on Pardus, since it is new to India. The range runs XXS to XL on the Spark Sport and Super Sport Gen2, XXS to L on the Super AL, and only XS, S and L on the Gomera Ultra time trial frame. That last one is worth checking against your numbers before you commit, because the gaps between available sizes are wider than on the road models. Our Pardus model guide covers the full range.
What a chart cannot tell you
Worth being straight about this, because the tables above have real limits.
Height is a single number describing a body with at least four dimensions that matter: leg length, torso length, arm length and shoulder width. Two riders at 175cm, one with a long torso and short legs and one the reverse, will be comfortable on genuinely different frames. A chart cannot see that.
Flexibility matters as much as proportion. A rider who can hold a low position comfortably wants different stack from one who cannot, and that is a function of hamstring and lower back flexibility rather than skeleton.
Nor do charts account for what you are doing with the bike. The same rider might want a 56 for racing and a 57 for long-distance comfort.
Where the line sits: for a first bike or an entry-level purchase, a chart plus a test ride is usually enough. Above roughly ₹1,00,000, or if you are riding long distances, or if you have any history of knee, back or neck pain on a bike, a proper fit session before you buy will save you more than it costs, both in comfort and in not buying the wrong frame.
FAQ
What size bike do I need if I am 175cm tall?
Start at a 55 to 56cm road frame, or a medium. That is a starting range rather than an answer, since your inseam and torso length will move it and brands vary. Check the chart for the specific model before deciding.
How do I measure my inseam for a bike?
Barefoot, back to a wall, heels 15cm apart. Hold a hardback book between your legs and pull it firmly up against your crotch, keeping the spine level. Measure floor to the top of the book. Repeat three times and use the middle figure.
Is height or inseam more accurate for frame sizing?
Inseam, because it separates leg length from torso length. Height treats a long-legged and a long-torsoed rider of the same stature as identical, and they are not. Neither is as good as stack and reach.
What are stack and reach?
Stack is the vertical distance from the bottom bracket centre to the top of the head tube; reach is the horizontal distance between the same two points. They describe the frame independently of labels and components, which makes them the only reliable way to compare sizes across brands.
Should I size up or down if I am between sizes?
Size down for a more aggressive position or if you need standover clearance; you can fit a longer stem to recover reach. Size up for comfort or a long torso. The deciding factor is usually standover, because it cannot be adjusted at all, whereas reach can be changed with a stem.
Why is a 56cm frame from one brand different from another?
Sloping top tubes mean seat tube length no longer describes the bike, and manufacturers measure it differently, some centre-to-centre and others centre-to-top, a difference of 10 to 15mm. Compare stack and reach instead of the size label.
Does gravel bike sizing differ from road?
Not much. Most gravel frames follow road sizing within one size, though usually labelled S/M/L. Gravel geometry is typically slightly taller in stack and shorter in reach for the same nominal size, which puts you a little more upright.
Do I need a bike fit before buying?
For an entry-level bike, a chart and a test ride will usually do. For a significant purchase, long-distance riding, or if you have had knee, back or neck pain on a bike before, a fit session beforehand is worth it. It tells you the frame size to buy rather than leaving you to adjust around the wrong one.
Last updated: August 2026.
Unsure between two sizes? Give your height and inseam along with the model you are looking at to ask TBA Guide, or come to the shop in Kondapur for a test ride. Browse road bikes, gravel bikes and mountain bikes.
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