The Square Root Rule

Ian Lurie

Ever wonder if you could predict, with any accuracy at all, when you’ll hit diminishing returns on an advertising buy? It’s pretty important, yet almost impossible to figure out, or so you’d think.


It’s not actually all that hard, if you follow the square root rule. I’m not even going to try to explain it here though. Kevin Hillstrom has a far better explanation of the Square Root Rule than I ever will.

The important thing to note is that yes, all numbers can lie. If your marketing is totally ineffective, or if you lack baseline, historical data, chances are this formula won’t do you as much good.

Here it is again: The Square Root Rule, as explained by a Math Guy

Ian Lurie
CEO & Founder

Ian Lurie is CEO and founder of Portent and the EVP of Marketing Services at Clearlink. He's been a digital marketer since the days of AOL and Compuserve (25 years, if you're counting). He's recorded training for, writes regularly for the Portent Blog and has been published on AllThingsD, Smashing Magazine, and TechCrunch. Ian speaks at conferences around the world, including SearchLove, MozCon, Seattle Interactive Conference and ad:Tech. He has published several books about business and marketing: One Trick Ponies Get Shot, available on Kindle, The Web Marketing All-In-One Desk Reference for Dummies, and Conversation Marketing. Follow him on Twitter at portentint, and on LinkedIn at

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