Choose the finished width and length first. If the blanket will have a border, subtract that border on both sides to find the main panel size.
Panel width = finished width − twice the side-border width. Multiply the panel width by stitches per inch from a washed swatch, then adjust to the pattern’s stitch multiple and turning-chain instructions.
For example, a 40-inch blanket with a 2-inch border on each side needs a 36-inch panel. At 3 stitches per inch, the target is 108 pattern stitches before adjusting for the repeat. Do not add turning chains without checking whether the pattern counts them as a stitch.
Calculate length from row gauge separately. An unwashed chain is not a reliable measure of finished width, and yarn labels do not predict your personal gauge. Check the dimensions again after the first pattern section.
See blanket yarn choices for fibre and laundering trade-offs. Keep blankets and other loose bedding out of an infant’s sleep space.