Position of custom scroll track pointer

[amarprem]

TotalrecordCount = 300
Page size = 10
Pagecount = TotalrecordCount / Pagesize /* 30*/
One row size = 20px
Body size = 20px * pagesize
ScrollTrackSize = Body size /*200*/
ScrollPointerSize = Body size /Page count /*15*/
One row track size = 15 / 10; /*ScrollPointerSize / Page size = 1.5*/

My Problem is that if one row track size is floating number than i can't move the element with this value. Is there any logic to create this custom bar or Can i set position of element
to this float value . Please help me.

I use this logic to create custom scroll bar and retrieves records from server side as user scrolls.

If the One row track size is an integer number than there is no problem bcz i can move the ScrollPointer to this value.

Can any conversion can be done between px and pt or %?
Is there any other simple logic to create custom scroll bar?

I am begineer in javascript and css.
So please help me to find out this.