These days in our web meetings, everyone’s talking about two things: engagement and conversion. With emphasis on conversion; we want people to come to our websites and then do something. Give us their e-mail addresses. Sign up to receive a newsletter. Register for a drawing or a seminar. Buy something.

This makes sense. Of course, you want visitors to do something when they come to your website. We want that, too. We want you to be so impressed with us that you’ll contact us and hire us and pay us a lot of money to work for you. (So far, so good. Thank you. You know who you are.)

But as much as we want conversions, we can’t ignore engagement. We have to actually attract visitors to the site and engage them in something meaningful if we hope to convert them into customers.

We measure engagement lots of ways. How many people did we attract? How long did they hang around? What did they look at? How often do they come back?

All of these metrics are important–but, compared with conversion metrics, they’re soft. Anybody can attract a bunch of eyeballs to a website–just do something hilarious or shocking, and they’ll flock to your video. But can you attract the right people and keep them? And how much does it cost to do so?

This last question is one we don’t hear being explored very often. But we think it’s interesting. An interested, qualified visitor to your website is certainly worth something–and we’d suggest that the more time that visitor spends on your site, more more valuable he or she is. All things being equal, visitors who spend time on your site are more likely to think favorably of you, more likely to think of you if they’re in need of your goods or services, and more likely to convert on the site.

So one measure we’re looking at right now is cost of engagement: that is, how much are you spending per minute of time visitors spend on your website? How does what you’re spending on content, web updates, and socialization translate into minutes spent on the site by interested visitors?

For example, let’s say you’re spending $5,000 a month to develop blogs and videos and Facebook posts and update graphics. And, to keep it simple, let’s say you attract 2,000 visitors a month, and they spend an average of three minutes engaged with your content. You’re paying $5,000 for 6,000 minutes of engagement–or about 83 cents per minute someone spends on your site.

We actually prefer to take the measure one step further, to deep engagement. We do this by filtering the bounced traffic–that is, people who view only one page and leave the site–and applying the same formula. Continuing with the above example, let’s say your bounce rate is 50 percent–and the 1,000 visitors who don’t bounce spend an average of five minutes on the site. Measured this way, you’re spending $5,000 for 5,000 minutes of deep engagement, or a dollar a minute.

So: what should you be spending?

It depends on what you’re trying to do. If you’re selling high-ticket items, you should expect a relatively high cost of engagement. Your universe of potential buyers is smaller, and they’re going to take their time considering their purchases. If you’re a healthcare provider, a relatively high cost of engagement shouldn’t bother you. It makes sense to create and post great health content, because, in many cases, you’re hoping to develop long-lasting relationships with patients. You want to engage them and keep them coming back to you for advice–perhaps online at first, then in person.

But you do have to strike a balance. And it does make sense to work to lower the cost of engagement–which means either attracting more of the right kind of visitor, or finding ways to keep visitors engaged longer–or both. We’d suggest that it’s at least a metric you should be looking at: is your cost of engagement rising or falling? Should you be spending more to create even more engaging content? Or should you be spending less and trying to attract visitors in other ways?

We believe, fundamentally, that people who are actively engaged with the content on your site are your best customers and prospects. They are the visitors most likely to convert. That’s why working to up the depth of engagement while lowering the cost per minute–attracting more visitors and/or keeping them longer–is a valuable practice. And cost of engagement is a valuable measure of the effectiveness of your web marketing spending.