tl;dr
To determine which bike size do you need, first measure your inseam length in centimeters. Then, multiply the result by 0.7 if buying a road bike, 0.66 for a mountain bike, or 0.685 for a city bike. There are other things to consider, and these are discussed in this article.
Answering the question “What bike size do I need” isn’t as straightforward as it seems at first. There are many factors to consider, such as your height, inseam length, gender, and even personal preference. There isn’t a single bike size calculator that suits all riders, so your safest bet is to know exactly what to take into consideration when buying a new bike.
This article will teach you everything you need to know about how to choose a bike size, and will also give a couple of practical tips if you choose the wrong size bike. There will be specific sections for kids’ bikes, so feel free to scroll to these if that’s all you’re interested in:
Table of contents
Choose a Bike Size Based on Your Height
The good part is that you can base your decision entirely on your height. We always recommend going into your local bike shop and trying out a couple of options, but not everyone has that luxury.
Height is also a bulletproof value because it’s hard to measure wrong, and you likely know it already. It’s tricky if you’re in-between sizes and have no previous bikes as a point of reference. If that’s the case, we really can’t recommend enough visiting your local bike shop.
Anyhow, the following table provides a summary of height to frame size relationship in both centimeters and inches - for mountain bikes:
| Your height (cm) | Your height (inch) | Frame size | Frame size marker |
|---|---|---|---|
| 150 - 160 cm | 4'11" - 5'3" | 13 - 15 inches | XS |
| 160 - 170 cm | 5'3" - 5'7" | 15 - 16 inches | S |
| 170 - 180 cm | 5'7" - 5'11" | 16 - 17 inches | M |
| 180 - 188 cm | 5'11" - 6'2" | 17 - 19 inches | L |
| 188 - 193 cm | 6'2" - 6'4" | 19 - 21 inches | XL |
| 193 and up cm | 6'4" and up | 21+ inches | XXL |
For example, if you’re 185 cm tall, a mountain bike frame size between 19 to 21 inches (or XL) will fit like a glove.
Different manufacturers measure frame sizes differently, which is something to keep in mind. Our recent article will tell you more on this topic:
And below is the exact same table but for road bikes:
| Your height (cm) | Your height (inch) | Frame size | Frame size marker |
|---|---|---|---|
| 147 - 157 cm | 4'10" - 5'2" | 48 cm | XXS |
| 157 - 167 cm | 5'2" - 5'6" | 50 cm | XS |
| 160 - 167 cm | 5'3" - 5'6" | 53 cm | S |
| 167 - 175 cm | 5'6" - 5'9" | 55 cm | M |
| 175 - 183 cm | 5'9" - 6'0" | 58 cm | L |
| 183 - 191 cm | 6'0" - 6'3" | 60 cm | XL |
| 191 - 198 cm | 6'3" - 6'6" | 63 cm | XXL |
You can see that road bike frames are measured in centimeters or marker sizes (XXS-XXL). It’s uncommon to see a road/gravel bike size written in inches.
And that’s the basic height for you. Keep in mind that these tables are very generic and they might not be the best fit among all bike manufacturers. Visit a local bike shop, or investigate the manufacturer’s website for more information.
Next, let’s go over another way to find out what size bike you need, and that’s by measuring your inseam length.
Calculate Inseam Length for Choosing a Bike Size
Inseam length represents the length of the inner side of your leg. Measuring it is a three-step process:
- Take off your shoes and stand on a flat surface with your legs about 15 to 20 cm (6" to 8") apart.
- Measure the height from the ground to your crotch.
- Use the formula to calculate the right bike size.
More on the formula in a second, but first, take a look at the following image to know exactly what you should measure:
Credit: Bike Lock Wiki
Now, to the formula. You should multiply the inseam length in centimeters by one of three possible factors, depending on the type of bike you’re buying:
- Road bike: Inseam length in cm x 0.7
- Mountain bike: Inseam length in cm x 0.66
- City/Touring/Trekking bike: Inseam length in cm x 0.685
Here are a couple of examples to guide you:
- Road bike with 85 cm inseam - 85 x 0.7 = 59.5 = 60 cm
- Mountain bike with 31" inseam - (31 x 2.54) x 0.66 = 52 cm or 20.5"
- City bike with 60 cm inseam - 60 x 0.685 = 41 cm or 16"
Inseam length is the best way to calculate the bike size you need because it doesn’t assume all people are built equally. Two people of identical height can have significantly different inseam lengths.
Keep that in mind when looking for your next bike.
Bike Size Charts
Some of the values might overlap, but that’s because people of identical heights can have different inseam lengths. Think of these values only as rough guidelines. It’s always better to consult with your local bike shop or checking out manufacturer-specific measures on their website.
Mountain bike
| Your height (cm) | Your height (inch) | Leg inseam (cm) | Leg inseam (inch) | Suggested size (inch) | Suggested size (marker) |
|---|---|---|---|---|---|
| 148 - 158 cm | 4'10" - 5'1" | 61 - 73 cm | 24 - 29" | < 14" | XS |
| 158 - 168 cm | 5'1" - 5'5" | 63 - 76 cm | 25 - 30" | 15 - 16" | S |
| 168 - 178 cm | 5'5" - 5'9" | 66 - 78 cm | 26 - 31" | 16 - 17" | M |
| 178 - 185 cm | 5'9" - 6'0" | 68 - 81 cm | 27 - 32" | 17 - 18" | L |
| 185 - 193 cm | 6'0" - 6'3" | 71 - 83 cm | 28 - 33" | 18 - 19" | XL |
| 193 - 198 cm | 6'1" - 6'6" | 73 - 86 cm | 29 - 34" | 19" and up | XXL |
City bike
| Your height (cm) | Your height (inch) | Leg inseam (cm) | Leg inseam (inch) | Suggested size (inch) | Suggested size (marker) |
|---|---|---|---|---|---|
| 148 - 158 cm | 4'10" - 5'1" | 61 - 73 cm | 24 - 29" | 14" | XS |
| 158 - 168 cm | 5'1" - 5'5" | 63 - 76 cm | 25 - 30" | 15" | S |
| 168 - 178 cm | 5'5" - 5'9" | 66 - 78 cm | 26 - 31" | 16" | M |
| 178 - 185 cm | 5'9" - 6'0" | 68 - 81 cm | 27 - 32" | 17" | L |
| 185 - 193 cm | 6'0" - 6'3" | 71 - 83 cm | 28 - 33" | 18" | XL |
| 193 - 198 cm | 6'1" - 6'6" | 73 - 86 cm | 29 - 34" | 19" | XXL |
Road bike
| Your height (cm) | Your height (inch) | Leg inseam (cm) | Leg inseam (inch) | Suggested size (inch) | Suggested size (marker) |
|---|---|---|---|---|---|
| 148 - 158 cm | 4'10" - 5'1" | 61 - 73 cm | 24 - 29" | 47 - 48 cm | XS |
| 158 - 168 cm | 5'1" - 5'5" | 63 - 76 cm | 25 - 30" | 49 - 51 cm | S |
| 168 - 178 cm | 5'5" - 5'9" | 66 - 78 cm | 26 - 31" | 52 - 55 cm | M |
| 178 - 185 cm | 5'9" - 6'0" | 68 - 81 cm | 27 - 32" | 56 - 58 cm | L |
| 185 - 193 cm | 6'0" - 6'3" | 71 - 83 cm | 28 - 33" | 58 - 60 cm | XL |
| 193 - 198 cm | 6'1" - 6'6" | 73 - 86 cm | 29 - 34" | 61 - 63 cm | XXL |
Kids bike
| Age | Your height (cm) | Your height (inch) | Leg inseam (cm) | Leg inseam (inch) | Tire size (inch) |
|---|---|---|---|---|---|
| 2 | 85 - 90 cm | 2'9" - 3'1" | 30 - 35 cm | 12 - 14" | 10" |
| 3 - 4 | 90 - 100 cm | 3'1" - 3'3" | 35 - 42 cm | 14 - 17" | 12" |
| 4 - 5 | 100 - 110 cm | 3'3" - 3'7" | 42 - 50 cm | 16 - 20" | 14" |
| 5 - 6 | 110 - 115 cm | 3'7" - 3'8" | 45 - 50 cm | 18 - 22" | 16" |
| 6 - 8 | 115 - 120 cm | 3'8" - 4'0" | 50 - 60 cm | 20 - 24" | 18" |
| 7 - 9 | 120 - 135 cm | 4'0" - 4'5" | 55 - 63 cm | 22 - 25" | 20" |
| 9 - 11 | 135 - 145 cm | 4'5" - 4'9" | 60 - 72 cm | 24 - 28" | 24" |
| 11 - 14 | 145+ cm | 5'0"+ | 72+ cm | 28"+ | 26" |
What If You Buy a Wrong Size Bike?
It’s ideal to get the bike size right when purchasing the bike because the frame is the only part you can change. That being said, it’s not the end of the world if you buy a slightly bigger or slightly smaller bike.
No one can help you if you’re 6'5" and bought a 54 cm road bike, though, so keep that in mind.
Here are a couple of practical tips to make your slightly smaller/bigger bike more comfortable:
Send it back and order the right size. If you’ve just bought the bike from an online store, chances are you can return it and get a bigger/smaller one without a fee. Most web shops have a free return window, so it’s an option worth exploring.
Move the saddle to the front or rear. If you’re feeling like your knees aren’t aligned with your toes when the crank is in a 3’o clock position, experiment with saddle setback. Chances are you won’t get it perfect, but even small alterations can have a significant impact to ride quality and can prevent injuries down the road.
Buy a longer/shorter stem. In case your arms are too flexed, consider buying a shorter stem. If your arms are extended all the way and start hurting in the wrist and elbow area, a shorter stem might help you get rid of the pain.
Buy a longer seat post. If you can’t pull out the seat post any higher due to the safety area, consider buying a new one. It’s a worthy investment if your saddle height is too low, and the current seat post doesn’t allow you to make it any higher.
What If You're In-Betwen Sizes?
Then it’s just up to personal preference.
It’s common to see riders being in-between sizes. Some manufacturers offer frame sizes in this category as well, such as M/L. Not all of them do, so we recommend going to a local bike shop and trying out a couple of sizes of the same bike.
Here’s some general guidance for when you’re in-between bike sizes:
- Looking for a more agile bike? Consider going a size down.
- Looking for more stability for longer rides? Consider going a size up.
Summing up What Bike Size Do I Need
To summarize, what bike size you need depends mostly on your height and inseam length. We showed you how to work with both to choose the perfect road/gravel, city, and mountain bike.
If you’re in-between sizes, it’s worth paying your local bike shop a visit and trying out the same bike in different frame sizes. For example, if you’re somewhere between M and L, try both and see what fits you and your riding style the best. Some manufacturers even have dedicated frame sizes for these riders (e.g., M/L), but those are few and far between.
