I will have a go with an example.Unfranked dividend = $100Full...

I will have a go with an example.

Unfranked dividend = $100
Full Franked (30%) Dividend = $70

so to get from 70 to 100 need to times by approx 1.43

eg multiplier = (1-(frank%*0.30)/0.70)

if 0% paid i.e unfranked multiplier = 1.429
if 50% paid then multiplier = 1.21
if 75% paid then multiplier = 1.107
if 100% paid then multiplier = 1

so if I recieved

an unfranked dividend of $1.429 its the same as a $100 fully franked dividend.

The real value actually depends on your Tax level, so you better work out whats best here as well.