Sizing your bike correctly is important, but it’s especially crucial when choosing a mountain bike. You need a pair of wheels that can provide the support and safety you need while tackling trails and off-road adventures.
A properly sized mountain bike improves your handling and balance while reducing the risk of injury and long-term strain. With so many frame sizes, body measurements and riding styles to think about, finding the right fit can seem overwhelming.
But it doesn’t have to be. In this mountain bike sizing guide, we’ll walk you through the exact steps to determine your ideal fit based on your height, inseam and riding goals.
You can also check out our guide to electric mountain bikes.
Why Mountain Bike Sizing Matters
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Comfort: A correctly sized bike supports the natural mechanics of your body. By getting into a relaxed and efficient position, you’ll reduce the strain on your back, shoulders, wrists and knees.
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Control: Fit affects how well you can manoeuvre the bike, especially on technical trails or steep descents.
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Power Transfer: The right fit produces a smoother and more responsive ride by making sure that your energy is transferred efficiently into each pedal stroke.
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Injury Prevention: Riding a bike that's too large or too small increases the risk of overuse injuries and even crashes due to poor handling.
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Confidence: When your bike feels like an extension of your body, you’ll ride more confidently and be able to push your limits.
How to Measure Yourself for the Perfect Bike Size
Step 1: Measure Your Inseam
Your inseam is the most important measurement for determining the correct frame size. It determines your stand over height, which is the clearance between the top tube and your body when standing over the bike.
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Stand barefoot against a wall with your feet 15-20cm apart.
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Place a hardcover book or level object between your legs to simulate a bike saddle.
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Measure from the floor to the top edge of the book/spine. This is your inseam length.
Step 2: Measure Your Height
Height is the most commonly used metric in mountain bike sizing, but it’s most effective when paired with inseam measurements. This gives a more complete picture of your proportions. Riders of the same height can have different leg lengths or torso proportions, which is why it’s only part of the equation.
How to measure:
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Stand against a flat wall without shoes.
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Keep your feet together, back straight and look forward.
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Mark the highest point of your head with a pencil or piece of tape.
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Use a tape measure to determine the distance from the floor to the mark.
Step 3: Measure Your Reach and Arm Length
Reach and arm length are often overlooked, but they’re crucial for a good handlebar position. A bike that’s too short can feel cramped, while one that’s too long can overextend your arms, causing fatigue or shoulder pain.
How to measure reach:
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Extend one arm straight out to the side, parallel to the floor.
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Measure from the centre of your sternum (chest bone) to the tip of your extended fingers.
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This number is your functional reach.
Understanding Mountain Bike Sizing Charts
Once you’ve taken your key body measurements, t’s time to match those numbers to a mountain bike size. Most manufacturers will have general size recommendations that translate your body dimensions into frame sizes, usually labelled as Small (S), Medium (M), Large (L), etc.
A typical mountain bike height guide looks something like this:
| Rider Height | Inseam (cm) | Frame Size (inches) | Size Label |
| 152–160 cm | 65–73 cm | 13–15” | X-Small |
| 160–170 cm | 70–78 cm | 15–17” | Small |
| 170–178 cm | 76–84 cm | 17–19” | Medium |
| 178–185 cm | 82–89 cm | 19–21” | Large |
| 185–193 cm | 87–95 cm | 21–23” | X-Large |
Frame Size vs. Wheel Size
Many first-time riders confuse frame size with wheel size, but they serve very different purposes in mountain bike fit and performance.
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Frame Size refers to the length of the seat tube and determines how the bike fits your body.
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Wheel Size refers to the diameter of the wheels (e.g., 27.5", 29") and affects how the bike rides and handles.
Sizing Differences Across Brands
It’s important to know that not all brands size their mountain bikes the same way. A Medium frame from one brand may feel like a Small or Large from another. This is because geometry (such as top tube length, standover height and reach) can vary depending on the bike’s design philosophy.
Always check the manufacturer’s specific size chart for the model you're considering and pay attention to geometry charts, not just the size label (S, M, L).
Test Ride: The Best Way to Ensure a Perfect Fit
No matter how precise your measurements or how detailed the sizing chart, the best way to get the right mountain bike size is to test ride the bike yourself.
During a test ride, pay close attention to the following:
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Comfort: Do you feel natural and relaxed while seated and pedalling?
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Reach: Are your arms comfortably extended, or are you overreaching or cramped?
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Handling: Does the bike respond well to your inputs when turning or tackling hills?
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Standover Height: Can you comfortably stand over the frame with both feet flat on the ground?
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Pedalling Efficiency: Are your legs fully extending with a slight bend at the bottom of the pedal stroke?
Ready to Find Your Perfect Mountain Bike?
You're now equipped with everything you need to confidently choose the correct size of MTB. The only thing left to do?
Explore our full range of mountain bikes here.
Not sure which bike is best for you? Get in touch with our team and we’ll be happy to help you find your perfect ride.
