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I saw this topic come up in a designer’s forum on ravelry, and I feel that this should be stated very very clearly:
IF YOU DO NOT MATCH THE PATTERN’S GAUGE, THE AMOUNT OF YARN YOU NEED WILL VARY FROM WHAT THE PATTERN SAYS.
Even if you DO match the gauge, yarn amounts can vary a good 10% or so (which is why the yarn amounts listed in my pattern have “padding”).
Let’s pretend your stitch gauge or row gauge is larger than what the pattern says. That means your stitches are bigger or fatter than the designers stitches. Consequently they take up more yarn. This means you will need more yarn to do, say, 63 rows of the pattern than the designer did. It also means your finished item will be a completely different size, but that’s a post for another day.