Take one quarter of the total cast on stitches. (or divide it by 2, then by 2 again--I'm not sure if this is always the same as dividing it by four) This number is the same as the number of rows tall your heel will be. You can take this number and multiply it by your swatch to figure out the height in inches.
Short rows are knit flat, and in my opinion are the simplest way to knit a heel. However, I hear a lot of knitters grumble about short rows or tutorials sold as "you don't even have to do short rows!" so YMMV. I'll detail how to do short rows below:
Just keep knitting 👍
The toes will be the same length as the heel, so just keep knitting until you only have that much left.
🎊🏆🏆🏆🏆🏆🎊