I have a lot of patterns for dishcloths that I would like to make into afghan sizes and baby blanket sizes. Is there a formula for increasing a crochet pattern or decreasing a pattern.
Without seeing what your dishcloth pattern looks like, I can try to give some general advice.
Most crochet patterns have a section that repeats, then some number of chains that is needed to get started. That's why many crochet stitch patterns says to begin by chaining a multiple of X plus Y sts.
If you can figure out what that X and Y are for your dishcloth pattern, then you can extrapolate and make an afghan or baby blanket out of the same pattern.
For example, if it seems like the dishcloth pattern is over a multiple of 3 sts plus 4, then you just need to determine how many multiples of 3 will get you the width that you want for your afghan or blanket and add the chain 4.
Assuming the dishcloth is 14" wide or so, multiplying it by 5 will give you approximately a 70" wide afghan...
Many well-written patterns will provde the stitch pattern in a generic form (thereby providing the "mult of X plus Y" instruction needed) separately from the specific instructions for the project.
Hope that helps!