Crochet Cotton for doilies

[Daisy Jean]

I have doily patterns that call for size 20 crochet cotton and prefer to use size 3. Does anyone have any idea approximately how much larger my doily would be?

[Granny Square]

Welcome to the 'ville!  That is a really interesting question.  I mostly make doilies nowadays--thread is cheap, I think they're pretty and I like to 'fiddle' with the designs on occasion.  I mostly use size 10, even for vintage patterns that call for 20 or 30, and just let the size fall where it may.

Some vintage patterns I've seen would give dimensions for a doily with different thread sizes (10, 20, 30) but not as big as size 3.

The only thing I can think of to compare wraps per inch, and I found a site with that info for thread; size 3 is 24 WPI and size 20 is 50 WPI, so size 3 is pretty much twice as thick as size 20.  The thing is, my gauge and the designer's gauge for doilies (and anything else) often are not the same (and go either way), with is certainly not unique to me, so this is just a rough ballpark way to guess that your doily should be about 2x the size the pattern says it should be with size 20 thread.

edited to add, depending on the hook too I suppose; not sure if that works in a linear way, meaning it works if your hook is also 2x the measurement of the one called for...maybe swatching is the answer.  Work the first few rounds in your #3 thread and try to figure out the % that diameter is, to the rest of the doily per the pattern photo and do a little math to extrapolate the final size?  Not sure how accurate that would be, probably reasonably so if the pattern is more or less consistent in stitch height.

Edited November 1, 2022 by Granny Square