QR Code capacity with fixed rendered size and dynamic data

There's a paper forms barcode and symbology is QR Code, layout is 46mm x 46mm, error correction level is M, module width is 0.592mm, and max capacity is Chinese(UTF8) x 88 or number x 627 or uppercase A x 380 or lowercase a x 263, and QR code renered size is about 30mm x 30mm when max capacity.

So, my question is, if I want to ALWAYS keep this QR code renered size is same as max capacity(30mm x 30mm), but my daya is dynamic and mix numeric, alphanumeric and byte mode, is there any formula to calculate how may character such as space should be appended?

thanks