Really what you care about is the ratio of wingspan to body length in the kind of moth you’re creating. There are a lot of different kind of moths out there. Find the one you like, then math it out.

• Find your ideal moth
• Google that moth’s wingspan, “A”
• Use a tool like maybe pixels in a line or even a ruler against your computer screen to find the ratio. You want wingspan, “W” and height “H”
• The ratios of real world measurements to what shows up on your screen will be roughly the same, so A/W = X/H. You can find the approximate real world height with X = H * A / W

Or just look at the moth and make a best guess. Anyone who calls you out can do the math themselves ;p

I think you’re looking for “thorax length” or “body length”, as different publications list it differently. It’s possible that “height” as a search term might be throwing off what you get back.

One of the largest moths in the world has a wingspan of up to 11 inches and a body length of up to 6 inches, a ratio of about 1.833:1. One of the smallest has a wingspan of up to .63 inches and a body length of up to .28 inches, a ratio of about 2.25:1. Something in that range, or along that distribution curve, is probably a good way to go when creating this creature for your project.

I don’t know the precise answer, but how I would approach this if I could only find the wing span is I’d look up a bunch of photos, like the one you’ve supplied, and measure the ratio of body length to wingspan in pixels. Then you can apply that ratio to the average wingspan that you are able to find. Would it be 100% accurate? No. Would it be good enough for an RPG? For any character or species I’d make I think it’d be close enough. But that’s for you to decide.