Cycle Size Calculator

Road Bike (Racing/Tarmac) Mountain Bike (MTB/Off-road) City / Hybrid / Trekking Bike

Measure from your crotch to the floor while standing straight.

Recommended Frame Size

function calculateCycleSize() { var inseam = parseFloat(document.getElementById('inseamLength').value); var type = document.getElementById('bikeType').value; var resultDiv = document.getElementById('resultArea'); var frameText = document.getElementById('frameResult'); var categoryText = document.getElementById('sizeCategory'); if (isNaN(inseam) || inseam <= 0) { alert("Please enter a valid inseam measurement in centimeters."); return; } var size = 0; var unit = " cm"; var label = ""; if (type === "road") { // Formula: Inseam x 0.665 size = Math.round(inseam * 0.665); unit = " cm"; if (size < 48) label = "Extra Small (XS)"; else if (size <= 51) label = "Small (S)"; else if (size <= 54) label = "Medium (M)"; else if (size <= 57) label = "Large (L)"; else if (size <= 60) label = "Extra Large (XL)"; else label = "XXL / Custom"; } else if (type === "mtb") { // Formula: (Inseam x 0.67) – 10-12 cm, then convert to inches // We use standard average (Inseam * 0.67 – 11) / 2.54 var cmSize = (inseam * 0.67) – 11; size = (cmSize / 2.54).toFixed(1); unit = " inches"; if (size < 15) label = "Extra Small (XS)"; else if (size <= 16.5) label = "Small (S)"; else if (size <= 18.5) label = "Medium (M)"; else if (size <= 20.5) label = "Large (L)"; else label = "Extra Large (XL)"; } else if (type === "city") { // Formula: Inseam x 0.685 size = Math.round(inseam * 0.685); unit = " cm"; if (size < 48) label = "Small (S)"; else if (size <= 54) label = "Medium (M)"; else if (size <= 59) label = "Large (L)"; else label = "Extra Large (XL)"; } frameText.innerHTML = size + unit; categoryText.innerHTML = "Standard Designation: " + label; resultDiv.style.display = "block"; }

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The Importance of Correct Cycle Sizing

Choosing the right bicycle frame size is the most critical decision you will make when purchasing a new bike. An incorrectly sized bike doesn't just feel awkward; it can lead to chronic pain in the lower back, knees, and wrists. It also affects the handling, stability, and safety of the cycle.

How to Measure Your Inseam Correcty

Your inseam for cycling is different from your trouser inseam. To get an accurate measurement for the calculator:

1. Stand against a wall in your socks (or barefoot).
2. Place a thin hardcover book between your legs, flat against the wall, and pull it up until it is firm against your crotch (mimicking the pressure of a saddle).
3. Have someone measure from the top edge of the book to the floor in centimeters.
4. Ensure the measuring tape is perfectly vertical.

Understanding Bike Types

Different styles of riding require different geometric configurations:

• Road Bikes: Measured in centimeters (cm). These frames are designed for aerodynamics and efficiency. A tighter fit is often preferred for competitive riding.
• Mountain Bikes (MTB): Measured in inches. These frames have a lower top tube to allow for body movement over rough terrain. They generally run smaller in numerical value than road bikes.
• Hybrid/City Bikes: These prioritize comfort and an upright position. They are usually measured in centimeters and have more forgiving geometry.

Example Size Guide

Inseam (cm)	Road Frame (cm)	MTB Frame (in)
75 cm	50 cm	15-16″
80 cm	53 cm	17-18″
85 cm	57 cm	19-20″
90 cm	60 cm	21-22″

What if you are between sizes?

If your measurements put you exactly between two frame sizes, the general rule of thumb depends on your "Reach" (upper body length). If you have a long torso relative to your legs, go for the larger size. If you have shorter arms or prefer a more upright, comfortable ride, choose the smaller size. A smaller frame is usually easier to adjust using a longer seat post or stem.