One cell represents one stitch. The width and height come from your measured gauge, so you can sketch a motif in the proportions of your own fabric.
Start with your measured gauge
Count stitches and rows over a measured distance with the yarn, hook and stitch you intend to use. Enter 10 cm or 4 inches as actually measured: 4 inches equals 10.16 cm.
Print at actual size
Choose 100% or Actual size in the print dialog, with the matching paper and orientation. Measure the 50 mm calibration line. Fit-to-page printing changes the size of every stitch cell.
Scale and cell shape
At 16 stitches and 18 rows per 10 cm, a 1× cell is 6.25 mm wide and about 5.56 mm tall. Choose 2× to draw larger: the paper doubles the cell size, not the finished project.
Flat charts and rounds
Row 1 is numbered at the bottom. This is a rectangular planning grid, not a simulation of stitch lean or a complete pattern. Flat rows alternate reading direction; unturned rounds keep the same direction. Check your technique with a swatch.
Method and further reading: Vanessa Smith Designs