This is easily adapted to adult sizes. Using size 9 needles and a skein and a half of yarn, knit a square that's seven by eight inches, and then sew the sides three inches up from the bottom and two inches down from the top.

Tools and Materials

Size 6 needles
1 skein merino yarn
1 yarn needle

Child's Knit Hand Warmer How-To

1. Cast on 36 stitches (6 inches) with 2 strands of yarn (use thicker wool and only 1 strand for adult-size version, which yields 7 inches). Knit every row for 80 rows (7 inches) -- or for adults 65 rows (8 inches).
2. Cast off. Weave in all ends.
3. Stitch together along selvedge from bottom up to 3 inches and from top down to 2 inches to create thumb opening, above.

Merino light yarn, in Well Water, by Madelinetosh, from purlsoho.com. For adult hand warmers Merino, alpaca, and silk yarn, in Lichen, by Organic, from fiberco.com.