Number of people touched x depth of impact x time = social impact.

He was about to go for his PhD when he had an aha moment.

"I started thinking about what it would take to write a PhD. And I'd be lucky if maybe 50 people read it," he told attendees at the prestigious Churchill Club annual award ceremony in Santa Clara, California, on Thursday, where he was being honored with the 2016 Global Benefactor award.

"Simply writing a PhD or academic book was unlikely to play much of a role in helping shape people's lives as I wanted," he said. So he looked around and reasoned that writing software would be able to influence more people.

He learned to code, landed a job at Apple, then at Fujitsu. Then founded an online dating startup, SocialNet, which failed. He then joined PayPal before it sold to eBay for $1.5 billion in 2002. After that, as a member of the so-called PayPal mafia, he founded LinkedIn.

The idea of how to best influence change stuck with him. He came up with a formula for it:

Number of people touched x depth of impact x time = social impact.

He's used that simple formula to choose startup ideas and to help decide how to spend time and money as they grow.

But he says everyone can use that formula to spark change, be happier, and create more successful businesses that really affect lives.

The secret is this: volunteering. Not just any old volunteering, but using your expertise in an area that you care about and ramping up your efforts every year.

That's what he did. At Apple, "I started joining nonprofit boards to make a significant difference," he said. For instance, he joined an organization that taught underprivileged teens about using the internet.

And he simply kept going from there.

"Each year, I ask: Now that I have this knowledge, these resources, what can I do?" he said.

Volunteering allows anyone to have a bigger impact, he believes, because "you can contribute and amplify."

It's a nice thought: Give away your time, amplify the organization's work, change the world, and be a happier person in a happier world.

Wait, Reid knows how to code?