UX Virality Week: 3 of 7

One part of virality that I rarely see anyone discussing is how the format of the viral thing, and how that changes the way it spreads. The way something spreads also effects the number of people it can reach, so today we will learn about:

Transmission & K-Factor


(If you missed the first two lessons, start here.)

Every tv show or movie that deals with a virus includes a scene where board-room bureaucrats learn how the virus is transmitted from one person to another.

It could be air-borne, covering a large area but getting weaker with distance. It could be in the blood, which makes it hard to spread, but very effective when it does. Or it could spread through silly dancing at concerts or in nature.

Viral products and content work the same way, metaphorically.

Maybe you have to invite a specific person directly — like Dribbble —which spreads more slowly, but probably comes with more credibility.

Maybe it’s a photo or video that you can post on Facebook or Twitter. Easy to spread and understand, but doesn’t last very long.

Or maybe using the product itself is viral — like email — where every mail let’s people know that your messages was “sent from Hotmail”.


Make it very contagious.

When you get the flu, the best thing you can do is stay home from work, to prevent other people from getting sick.

When we design a virus, we want the opposite. We want as many people to get it as possible. 

If every person that gets the flu makes two other people sick, your whole office will become snot factories in a few days.

If every person only makes 0.5 other people sick (on average) you might not even notice.

Think about that: the difference between spreading 2 people at-a-time and 0.5 people at-a-time is the difference between an epidemic and nothing.

That number is called a K-Factor.

The “tipping point” for a virus is a K-Factor of 1.

Anything higher than 1 and it will spread exponentially. Anything lower, and it will slowly fade away.

Generally speaking, the more “invites” or “shares” something gets, the higher the K-factor will be. 


As a UX designer: your goals will determine which viral strategies are best for you.

Dribbble is a community where quality matters, and growing super-quickly might actually hurt that quality, so they give more invites to people who post popular stuff. That makes the quality viral, and Dribbble more credible, even though the site grows more slowly.

Buzzfeed, on the other hand, doesn’t give two shits about quality. They are all about pageviews. So everything they do is based on catchy headlines, funny pictures, and quizzes to see which category of irrelevant nonsense you are.

Dribbble has grown into a strong, loyal — not-so-big — community of designers that influences trends. Buzzfeed makes craptons of money, but they have no loyalty or credibility at all.


Making your creation super easy to spread is one thing, but it’s more helpful if you can recruit people to spread your design for you.

Tomorrow we why letting people change your content or product can make it more viral than any feature you could design: Designing Adaptability.