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Bicycle handlebar dimension standards

This post will give overview of bicycle handlebar size standards, in terms of stem mounting area as well as grip mounting area (or bar wrap area for road “drop” bars). Other important dimensions of road bike bars are explained in the post about road bar geometry, while important considerations for flat bars are given in MTB (flat) bars setup post.

1. Measuring important diameters

If handlebars are sought for a stem already owned, look at stem size standards for how to take important measurements. For the handlebars themselves, it is important to measure the following two diameters: stem clamp diameter and grip diameter. Picture 1 shows how to measure the stem clamp diameters of flat and drop bars.

Measuring the other important dimension, grip diameter, is shown in picture 2.

The pictures 1 and 2 speak for themselves, no need for further explanation. Standard dimension overview is given in the next chapter.

2. Standard bicycle handlebar sizes (diameters)

2.1. Stem clamp diameter standards

Current standards for stem clamp diameter are given in the table 1:

Handlebar attachment diameter – measurement units: mm (inches) Standard name
22.2 (7/8″)for steel bars of old MTB and BMX bikes
23.8 (15/16″)Obsolete British standard common on old British 3-speeds
25Obsolete French standard
25.4 (1″)Standard ISO size, common for bars from the end of the 20th century
26Italian road bike (and bar) standard. Obsolete
27Titan – obsolete standard
31.7 – 31.8 – depending on how manufacturers round down the inch dimension which is (1 1/4″)Modern “oversized” standard
35 (1 3/8″)Easton standard

2.2. Standard handlebar grip area diameters

There are only two current standard sizes:

  • Flat bars have a 22.2 mm (7/8″) grip area diameter.
  • Road (“drop”) bars have a 23.8 mm (15/16″) grip area diameter.

2.3. Overview of all (including obsolete) handlebar size standards

Table 2 gives an overview of all the handlebar size standards, with a short explanation of each.

Stem clamp diameterGrip diameterStandard explanation
mm (inches)mm (inches) 
22.2  (7/8)22.2  (7/8)Mostly steel bars of BMX and old mountain bikes.
23,8  (15/16)22,2  (7/8)Obsolete old British 3-speed standard, also used on old British steel drop bars.
2523,5Obsolete French standard.
25.4  (1)22.2  (7/8)Standard I.S.O. size, used on many flat bar bicycles at the end of the 20th century. Today mostly present on lower end models.
25.4  (1)23.8  (15/16)Standard I.S.O. size, used on many drop bar bicycles at the end of the 20th century. Today a bit less common, mostly used on low end models.
25.823.8  (15/16)Unofficial “in-between” size used by some Italian manufacturers so that the bars can be used with both ISO (25.4 mm) and Italian (26 mm) sized stems.
2623.8  (15/16)Old Italian standard for drop bars. Sometimes also called “road” standard.
26.423.8  (15/16)Old Cinelli drop bar standard. They switched to 26 mm in 1998.
2723.8  (15/16)Titan – obsolete drop bar standard.
31.8  (1 1/4)22.2  (7/8)Modern “oversized” standard for flat bars.
31.8  (1 1/4)23.8  (15/16)Modern “oversized” standard for drop bars.
35  (1 3/8)22.2  (7/8)Easton standard – for flat bar mountain bikes

Related post – Bicycle stem size standards:

Bicycle stem size standards (dimensions)
Bicycle stem size standards (dimensions)

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