Vinyl Replacement measurement’s
Before we learn how to install replacement windows it’s a must to get the dimensions correct. The existing window whether a aluminum or wood sash, they both have 2 measurements in every opening. Industry standards make the width before the height, in other words a window call out numbers that are 3-0 x 5-0, tells me it’s three feet wide by five feet high.
This cross section illustrates the inside bevel being the lower point of the new replacement window, and the top is square, so pull the tape to get both measurements and if not exactly the same then use the smaller dimension. To avoid having any extra work later on this is very important. The existing window jamb after removing all the sashes and parting beads (milled divider) gives you a block number to use and the manufacturer will make it square.