If you don't want to do the math yourself, there are a TON of speadsheets and brewing apps out there.
But for fun, here's a little trick I've heard quite a few times.
Use your desired mash temp, plus grain weight in pounds, plus 5.
Say 152F + 10 lbs + 5 = 167 should get you close. I believe that's for a room-temp mash tun.
You could play around with that, but I'd just find a calculator. It's very rewarding to see your mash temp fall right in line almost every time.