The Graham Number
One square root, two numbers off the financial statements, and a ceiling on what a careful investor should pay. It is the oldest quantitative valuation rule still in daily use — and, like every rule in this app, it is right often enough to be useful and wrong often enough to be dangerous. Here is where it came from, why it works, and exactly when it lies.
01Where it comes from
Benjamin Graham — Warren Buffett's teacher and the author of Security Analysis (1934) and The Intelligent Investor(1949) — spent his career trying to turn investing from a guessing game into an engineering discipline. He wanted a number a “defensive investor” could compute quickly and trust: a conservative estimate of the most you should pay for a stock without paying for hope.
The Graham Number is that estimate distilled to its simplest form. It answers a narrow but powerful question: given only what a company earns and what it owns, what is the highest price a cautious buyer should pay? Everything above that price is you betting on the future; everything below is a margin of safety.
02The formula
EPS is trailing twelve-month earnings per share — what the business actually earned. Book value per shareis shareholders' equity divided by shares — what the business owns, on paper, after debts. The Graham Number is the geometric mean of the two, scaled by 22.5.
That 22.5 is the whole philosophy hiding in a constant. Graham held that a defensive investor should never pay more than 15× earnings and never more than 1.5× book value. Multiply his two ceilings together — 15 × 1.5 — and you get 22.5. The square root simply blends the earnings test and the asset test back into a single per-share price. Buy below it and you have satisfied both of Graham's limits at once.
As Warren Buffett put it, “price is what you pay; value is what you get.” The Graham Number is the crudest, most durable line ever drawn between the two.
03What it looks like on a real stock
Enough theory. Here is the Graham Number doing its job on two names most Canadian investors know — computed from their latest filings.
The auto-parts maker trades roughly a third belowits Graham Number. By this one test it looks cheap — and the quality signals don't argue: return on equity near 11%, a current ratio of 1.9, and modest debt. That is what a Graham candidate is supposed to look like: unglamorous, tangible, and priced below what it owns and earns.
A household name, a fine business — and today it trades about 10% aboveits Graham Number. That doesn't make it a bad company or even a bad investment; it makes it a stock with no Graham margin of safety at this price. The number's job isn't to say “buy” — it's to tell you when you'd be paying up.
Same formula, two honest answers. The Graham Number is a filter, not a verdict — it earns its keep by being unsentimental about price.
04When the Graham Number lies
This is the part most explainers skip, and it's the part that matters most. The Graham Number is built on the assumptions of Graham's era — industrial companies with real, tangible balance sheets. Point it at the wrong kind of business and it produces a confident, precise, wrong answer.
Three places it breaks
- Banks & financials.A healthy Canadian bank routinely trades at 1.5–2× book with a high ROE. Since the formula caps book value at 1.5×, it will call almost every bank “overvalued” — meaningless for a business whose assets areloans. Graham's own defensive tests were never meant for financials.
- Asset-light & tech.A software or brand-driven company carries little tangible book value, so the Graham Number comes out tiny — and the stock looks perpetually expensive even when it's a superb compounder. The formula rewards factories, not intellectual property.
- No earnings, no number.If EPS is negative, you're taking the square root of a negative — there is no Graham Number. The method simply doesn't apply to unprofitable or deeply cyclical companies at the bottom of their cycle.
This is why the app never shows the Graham Number alone. It sits beside five other valuation methods and a company-type banner that warns you the moment you're looking at a financial, a REIT, or an unprofitable firm — precisely the cases above. One number is a data point; the spread of methods is the judgment.
See the Graham Number live on any stock
Every valuation above is computed fresh from the latest filings — no spreadsheet, no manual inputs. Open a stock and watch the Graham Number land next to five other methods and its margin of safety.