I measured my seat post on road bike to be 26.8mm
and found same model on ebay with same measurements

now I want to get a new seat post for my road bike

Do I have to find exact measurement of 26.8mm
or what measurements can i work it into?
i am thinkin within 26.5 to 28 mm? or how far bigger would fit and smaller?
perimeters i am looking for?

since post is 26.8 what would be the ideal size i should consider

Reason for want new seat post, I want one with more easier bolts to secure the saddle, as the one bolt thing is awkward at times.