The Ceiling Price Graham Refused to Pay Above
A stock trades at $80. The bulls insist it is worth $120. The bears say $50. Everyone has an opinion, nobody has a number. Benjamin Graham, the investor who taught Warren Buffett, distrusted opinions and built a formula instead, one that produces a single hard ceiling: the maximum price a defensive investor should ever pay. That ceiling is the Graham Number.
The formula is deliberately simple. It multiplies earnings per share by book value per share, multiplies that by 22.5, and takes the square root. The 22.5 is not arbitrary: it is Graham's two guardrails multiplied together. He believed a defensive investor should not pay more than 15 times earnings, nor more than 1.5 times book value, and 15 times 1.5 equals 22.5. The square root blends those two limits into one fair-value estimate that respects both at once.
Work an example. A company earns $5 per share and has a book value of $40 per share. Multiply: 5 times 40 times 22.5 equals 4,500. The square root of 4,500 is about $67. That $67 is the Graham Number, the most a conservative investor following Graham's rules should pay. If the stock trades at $80, it is above its Graham Number and offers no margin of safety. If it trades at $50, it sits well below, and the $17 gap is your cushion against being wrong.
That gap is the heart of Graham's philosophy. He called it the margin of safety, and it was the central idea of his entire approach. Buy a stock comfortably below its estimated fair value, and you are protected if your estimate was too optimistic, if earnings stumble, or if the market turns sour. The bigger the discount to the Graham Number, the more room for error you have bought yourself. A stock at $50 against a $67 Graham Number has roughly a 25% cushion. A stock priced exactly at its Graham Number has none.