A calculator makes the job go much faster. Also, the larger the swatch, the more accurate your measurements will be. If a schematic is provided for the knit pattern, photocopy it and write the results of your calculations and other notes right on the pattern. Do take lots of notes as you work on the item in case you decide to make it again some time in future. Measure your work regularly as you go and compare it to the original pattern, just to be sure your sizing is on track, and you should eventually come up with a comparable garment.
Knitters get a break here.
You'll generally need less yarn than stated when converting a crochet pattern to knitting. Remember, this is with the same yarn . You can't do a straight math calculation if you're substituting sport weight for worsted, etc. Always err on the side of too much yarn rather than too little no matter which way you're converting. Remember, you will get a comparable item , not an exact copy of the original pattern.