Bicycle Mechanics - handlebar clamp size

I'm trying to change out my bars..How can i tell what size clamp I have on my bike? I know it's not oversized 31.8--but what about 26 or 25.8? There's no size on the bar or the stem. I measured the bar around and came up with 8.5 cm around if that makes any sense. thanks

25.8 and 26.2 all are rounded up/down to 26. Same thing, different manufacturers label them as such.

25.8 and 26.2 all are rounded up/down to 26. Same thing, different manufacturers label them as such.

Ha, try fitting a 27.2 post on a 26.8 tube hole and let me know if they're the same.

Yea, they are definitely different though it will probably work in your applications. Think of like why the give you multiple Phillips screwdrivers in a set. The above would be a nightmare.

I suppose you can do math. Your circumference is 8.5 cm and you are looking for the diameter. The formula is 2(pi)r = C. 8.5/3.141592 = 2.705. So, that would mean you need something 27.05mm.

Now, besides revisiting middle school math, sometimes the size is stamped on the inside of the tube that is your handlebar on the edge.

Ha, try fitting a 27.2 post on a 26.8 tube hole and let me know if they're the same.
It's not the same issue. Handlebar clamps will tolerate minor diameter differences and 25.8 and 26.0 are considered interchangable. 25.4 in a 26.0 or vice-versa is considered too much of a mis-match but 25.8 and 26.0 are compatible.

I'd agree. You need some calipers. But you might get away with a ruler.

I'd agree. You need some calipers. But you might get away with a ruler.

Do YOU have a ruler that you can measure the difference between 26.0 and 25.8mm? That must be one mack daddy ruler!

With a ruler, it would actually be a difference of (26.0-25.8)*3.14 = 0.628mm. Certainly possible to measure. Easy way is to cut a strip of paper and wrap it around the bar. Mark and trim it to length to perfectly wrap around the bar. Then measure that paper with a ruler.