Three questions and you have the number. Pick the one that matches your trade, or use the general one.
Most calculators in this market multiply your missed calls by the value of a job and call the answer lost revenue. That is wrong twice over: it assumes every unanswered call was a customer, and that an agent would have won all of them. These ask you three things, make a cautious assumption about the rest, and show you every step if you want to see it. They will tell you when the numbers do not justify it.