Tape Measure

Tape measures are super handy when it comes to knitting. The sizing for many knitting patterns are based off of a specific number of stitches per inch and rows per inch. The specific number of stitches/rows per inch is called gauge. 

If the gauge of your knitted fabric does not match the recommended gauge of the pattern then your project will turn out a different size than expected. For example, if my gauge is tighter than the recommended than my project will turn out smaller, if my gauge is looser than recommended than my project will turn out bigger. To avoid this issue knitters often do a gauge swatch to see if they need to go up or down a needle size to meet gauge.