How to determine the correct frame size for a bike

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How to determine the correct frame size for a bike
Determine the Correct Frame Size for a Bike

Fit should be the main consideration when buying a new bike. After all, even the most expensive bike won't seem that great if it's too big or too small. Make sure you get a bike with a frame that fits you properly for maximum comfort when going on bike rides.

Skill level:


  1. 1

    Measure your inseam. This is best done barefoot. Stand against the wall and put a book between your legs so it pressed right up against your pelvic bone. Make a mark with a pencil on the wall along the top of the book. Measure the distance from the floor to the mark in centimeters.

  2. 2

    Use your inseam measurement to get a rough idea of your road bike size. Multiply your inseam by .65. This will give you a good estimate of your road bike size for bikes measured center to center. Thus if your inseam is 86 cm, you will fit a 56 cm road bike (86 x .65 = 55.9). Note that many road bikes are measured center to top. To determine how to fit these bikes, multiply your inseam by .67.

  3. 3

    Subtract an additional 10 cm and convert this measurement to inches to get your mountain bike frame size, roughly. Thus, if you fit a 56 cm road bike (c-c), you will fit a 46 cm -- or an 18 inch -- mountain bike.

  4. 4

    Consider top tube length. In many ways, this is the most important aspect of sizing a bike. Two 18-inch mountain bikes may have different length top tubes. Or a 54 cm and an 56 cm road bike may have the same length top tube. Given the same top tube length, the bigger bike may be more comfortable because it will allow you to get the bars up a bit higher.

  5. 5

    Know that women have longer legs and shorter top tubes than men. Unfortunately, most bikes are designed for men, and women often have a hard time finding a bike that will fit them well. Luckily, some manufacturers have begun to make women-specific models.

  6. 6

    Test ride some bikes once you have gotten a rough idea of what will fit you. This will help you determine what is most comfortable for you.

Tips and warnings

  • Your old bike is a great reference point. Measure the distance from the center of the bottom bracket to the top of your seat on your old bike. This assumes that you have your seat adjusted to the proper height. If in doubt, see the related eHow article, "How to Determine the Correct Saddle Height for Your Bike." Bring this measurement, along with your inseam measurement and a tape measure, when you go to look at new bikes.
  • Once you have the right size frame, you can fine tune the fit with different stems and bars.

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