Here's pattern for blanket square to knit, based on classic Red Cross pattern. The square produced is easy to join together. To increase, just knit into the front and back of the stitch.
The pattern doesn't really require a gauge since you just keep knitting garter stitch rows with one-stitch increases per row till the side reaches five inches, then start decreasing.
Cast on 1 stitch.
Row 1: k1, increase 1 in next stitch, knit to end of row.
Repeat Row 1 until side edge measures 5 inches (around 20 ridges using Red Heart high bulk acrylic on 4.0mm/US 6 needles).
Next Row: k1, k2 together, knit to end of row. Repeat this row until 1 stitches remain, cast off.
Note: Increases may be done on the last stitch of every row, until reaching desired size, then decreases done on last two stitches per row.
Gauge is 6 sts/inch, so for a regular square, cast on 30 stitches with 4.0mm (US6) needle.