calculating square footage for home office deduction

[gop1250]

I have an office in my home used exclusively for business (bookkeeping, client contact, etc) and a very large workshop onsite but unattached to my home.  Do I add the square footage of both my home and my workshop together and then figure out my office square footage or do I claim two separate home offices?  My utilities and other expenses are not separated.  If I did claim two different offices, how would I calculate utilities, insurance, mortgage interest etc?  I'm stuck. 

[RobertB4444]

For the total square footage of your home add the main home and the workshop together.

Then, for the square footage of the office, add the portions in the house together with the workshop.

This is an accurate representation of both your home and your office.

@gop1250