PhilBrew
Landlord.
... the online one at Brewer's Friend (link), leaving the defaults as is, will give you a fair indication ... if you scroll down and follow the links for calculating the wort correction factor for your refractomer you can see what might be involved in getting a more accurate measurement .. but BEWARE, that can end up consuming large amounts of time and effort ... which is why I only use my refractometer to assess that fermentation is finished, and then use a hydrometerThanks guys. I knew I should have asked about a calculator. Can you recommend one?
Cheers, PhilB