There's not a great way as private company financial information is not publicly available, though there are a variety of different ways to estimate. For a quick estimate, you can look them up on Manta.com, but their information should be taken with a grain of salt. Dun & Bradstreet company valuations are more accurate, but expensive, so unless you're doing it professionally, it's probably not worth the cost. You can also get hardcore and find out the basic size of the company (number of employees) and look up industry averages, revenues for companies of similar size, general profit percentage by industry, etc... Something tells me you don't want to get that involved. So I'd stick with Manta; you can always verify their information by looking up what they say the number of employees is and see if their data is out of date.