Twitter raised its share price range to $23 to $25 Monday but kept its offering size at 70 million shares. But Cramer is worried that institutional investors will pressure their brokers into buying as many Twitter shares as possible, only to turn around and sell them at a much higher price to retail investors.
"The big boys are betting that other, less informed investors—people who use Twitter and love it, people who don't know how to value the stock but just figure how can you go wrong—are going to come in and buy the stock from the professionals at much higher prices than they could hope to get on a pure valuation basis," Cramer said. "What I worry about are the people who think there's no price that's not worth paying for Twitter."
(Read more: Twitter 101: Mobile tips for the power user)
But Cramer told his "Mad Money" viewers that there is in fact a price at which Twitter is not worth owning: a valuation of $20 billion and no more. He arrived at that by taking into account what other companies would be willing to pay for Twitter, coupled with an effective discount to Facebook in terms of size and profitability.
Cramer blessed buying Twitter at no more than $28 a share but reminded investors not to buy the stock in the after-market, because that's almost always a losing trade.
—Reuters contributed to this report
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