Blanket Border Calculator

Why the two straight edges need different math

Along the top and bottom of a blanket, you're working border stitches directly into the tops of existing stitches, so the count follows your stitch gauge one-to-one. Along the left and right sides, you're working into row-ends instead, and a row-end is almost never the same width as a border stitch is wide — taller stitches like double or treble crochet pack more height into each row than a single crochet border stitch needs to match, so working one border stitch per row-end there would make the side edges flare and ripple. Skipping a row-end periodically (the ratios used here: roughly 3-in-4 for half double, 2-in-3 for double, 1-in-2 for treble) keeps the side edges lying flat against the body of the blanket.

Why corners don't need progressively more stitches each round

A circle needs continuously more increase stitches at larger radii because its whole circumference grows every round. A square corner is a fixed 90° turn, not a curve, so the classic "3 stitches into one corner stitch" trick works identically round after round without needing to grow — it's a self-sustaining rule, not an approximation that drifts as the border gets thicker. That's why this calculator's corner instruction stays the same regardless of how many rounds you work; only the straight-side stitch counts grow round to round, because each new round is worked into a slightly larger rectangle than the one before it.

A note on this being an estimate

Real blankets are rarely a perfect rectangle at the stitch level — tension can vary slightly across a large piece, and different colorwork or a scalloped edging pattern changes the effective stitch width. Work the first round, check that the piece is lying flat rather than cupping or rippling, and adjust a few stitches on a side before continuing if it isn't — that quick check is more reliable than trusting any calculation, including this one, to be exact down to the stitch.