I used my handspun for the mitts, not posative of the WPI on the yarn, since I gave the left over yarn away with the mitts,but I can tell you it was pretty much a heavy worsted weight. These mits are pretty stretchy & have fit everyone that has tried them on so far- including my 9-year-old daughter.
Pattern:
Using size 6 DPNs cast on 36 stiches. Join in the round and knit 15 rounds in knit 2 purl 2 ribbing. If you want longer cuffs to keep your arms warm, keep going until the cuff is as long as you want. Knit one more row of ribbing, placing markers between the 16th &17th stiches and the 18 &19 stiches.
Thumb Gusset:
Using size 6 DPNs cast on 36 stiches. Join in the round and knit 15 rounds in knit 2 purl 2 ribbing. If you want longer cuffs to keep your arms warm, keep going until the cuff is as long as you want. Knit one more row of ribbing, placing markers between the 16th &17th stiches and the 18 &19 stiches.
Thumb Gusset:
Next row: Knit ribbing up to the first marker, increase (knit front and back) in both stiches between the markers, continue ribbing to the end of the round.
Knit three rounds in ribbing pattern, knitting the stiches between the markers (Don't rib these stiches)
next row: follow ribbing until the markers, increase in the first and last stitches between the markers
Knit three rounds in ribbing pattern, knitting the stiches between the markers
Repeat the last four rows two more times. There will be ten stiches between the markers.
Knit one row in ribbing to the first marker. Place the stiches between the markers onto scrap yarn, and cast on two stiches in their place. Continue ribbing to the end of the round.
Knit three rounds in ribbing pattern, knitting the stiches between the markers (Don't rib these stiches)
next row: follow ribbing until the markers, increase in the first and last stitches between the markers
Knit three rounds in ribbing pattern, knitting the stiches between the markers
Repeat the last four rows two more times. There will be ten stiches between the markers.
Knit one row in ribbing to the first marker. Place the stiches between the markers onto scrap yarn, and cast on two stiches in their place. Continue ribbing to the end of the round.
Knit 30 rounds in ribbing, or until the mitts are long enough to cover your fingers. Bind off in pattern.
Place the thumb stiches on DPNs. Knit across the held stiches and pick up four stiches (the two stiches that were cast on for the hand portion and a stich on either side of them).
Join and knit in the round. When you get to four stiches that were picked up SSK, then K2Tog. You will now have 12 thumb stiches.
Knit five more rounds, or until the tumb length is approximately on your tumb joint.
Purl one round.
Knit one round.
Purl one round.
Cast off.
Weave in ends & enjoy! I didn't see the need to block these mitts, but if it makes you happy to block, then go for it :-) 
