Home office is used for storage of equipment i use for service, which is outside the house. how do i calculate % of usage in this scenario?

You would add the outside unit's square footage to the square footage of your house and then calculate the percentage of usage against this total.

I get that concept. There was another ? about how much do i use the home office for business. Some use it exclusively, such as an artist, service tech etc. + would answer 100%, while in my situation the actual usage is the storage. That's what I need help W. i was going to estimate 20% but could use guidance.

As it is exclusively used for storage for your business all the time you can actually claim 100% of that square footage .