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.

Only 26.8mm will fit.

Make sure that the 26.8mm you measured is accurate. Does it matched any engraved numbering on the post?
Also measure it at 3-different heights on the post.
And measure at the sides and at front/rear positions.
Total number of measurements 3 heights * 2 orientations = 6 measurements
Should be all 26.8mm. Otherwise take the area of largest measurement and see if it will slide down into the seat-tube.

the variations should only be in the thousandths of a MM..
[1st digit past the decimal Point is Tenths, second Hundredths , 3rd is thousandths ]


standard seat post sizes jump in 0.2mm increments. but rarely exactly 0.200mm ..