📌 “Valuation ratios are the basic tools for comparing stocks, but using the wrong one can lead you to wrong conclusions.” This article explains when to use P_E, P_B, and P_S ratios with simple examples.

Investors use valuation ratios to decide if a stock is cheap or expensive. The three most common ones are Price-to-Earnings (P_E), Price-to-Book (P_B), and Price-to-Sales (P_S). Each ratio looks at a different part of a company's finances. Choosing the right ratio depends on the company's situation.

Price-to-Earnings (P_E) Ratio: Measuring Profit Value

The P_E ratio compares a company's stock price to its earnings per share (EPS). It tells you how much investors are paying for each dollar of profit. A lower P_E can mean a stock is undervalued, but you must compare it to similar companies.

Example 1 Stable Tech Company
Company A: Stock Price = $100, EPS = $5.
P_E Ratio = $100 / $5 = 20.
This means investors pay $20 for every $1 of annual profit.
🔍 Explanation: A P_E of 20 is common for growing tech firms. If the industry average is 25, Company A might be relatively cheap. If the average is 15, it might be expensive.
Example 2 Company with No Profit
Company B: Stock Price = $50, EPS = -$2 (a loss).
P_E Ratio = $50 / -$2 = Negative (Not Meaningful).
🔍 Explanation: The P_E ratio fails when a company is losing money. You cannot use it. This is when you should look at other ratios like P_S or P_B instead.

Price-to-Book (P_B) Ratio: Measuring Asset Value

The P_B ratio compares a company's stock price to its book value per share. Book value is the net asset value (assets minus liabilities) from the balance sheet. It is best for asset-heavy businesses like banks or real estate.

Example 1 Commercial Bank
Bank X: Stock Price = $80, Book Value per Share = $100.
P_B Ratio = $80 / $100 = 0.8.
This means the stock trades at 80% of its net asset value.
🔍 Explanation: A P_B below 1.0 suggests the market values the company at less than its assets are worth. This could be a sign of undervaluation, or it could mean the assets (like old equipment) are overvalued on the books.
Example 2 Software Company
TechSoft Inc.: Stock Price = $200, Book Value per Share = $15.
P_B Ratio = $200 / $15 ≈ 13.3.
🔍 Explanation: A very high P_B is normal for tech companies. Their main value (software, brand, patents) is not fully captured on the balance sheet. P_B is less useful here; P_E or P_S would be better.

Price-to-Sales (P_S) Ratio: Measuring Revenue Value

The P_S ratio compares a company's stock price to its revenue per share. It is useful when profits are unstable, negative, or not the main focus, such as for high-growth startups or cyclical industries.

Example 1 Fast-Growing Startup
Startup Y: Stock Price = $30, Revenue per Share = $2.
P_S Ratio = $30 / $2 = 15.
This means investors pay $15 for every $1 of annual sales.
🔍 Explanation: A high P_S like 15 shows investors expect massive future growth from current sales. They are betting the company will become profitable later. Comparing P_S ratios within the same industry is key.
Example 2 Low-Margin Retailer
RetailCo: Stock Price = $40, Revenue per Share = $80.
P_S Ratio = $40 / $80 = 0.5.
🔍 Explanation: A low P_S (like 0.5) is common for low-margin businesses like grocery stores. They generate huge sales but very little profit per dollar of revenue. A low P_S doesn't automatically mean it's a bargain.

Summary & Comparison Table

P_E vs. P_B vs. P_S Ratio: When to Use Which
RatioFormulaBest Used ForKey Limitation
P_E RatioPrice / Earnings per ShareProfitable, stable companies (e.g., Coca-Cola, Microsoft).Useless for companies with zero or negative earnings.
P_B RatioPrice / Book Value per ShareAsset-heavy businesses (e.g., banks, insurance, real estate).Poor for companies whose value is not in physical assets (e.g., tech, services).
P_S RatioPrice / Revenue per ShareHigh-growth companies, startups, or firms with temporary losses.Ignores profitability; a company with high sales but no profit can still have a high P_S.

The table shows a clear rule: Use P_E for profits, P_B for assets, and P_S for growth or when profits are missing. Never use just one ratio in isolation. Always compare a company's ratio to its competitors and its own historical average.

⚠️ Common Pitfalls & How to Avoid Them

  • Comparing across industries: A tech stock P_E of 30 and a utility stock P_E of 15 does not mean the utility is cheaper. Different industries have different normal ranges. Always compare within the same sector.
  • Ignoring one-time events: Earnings can be inflated or deflated by a one-time gain or loss. Always check if the earnings used in P_E are "normalized" or recurring.
  • Using P_B for the wrong companies: A software company with a P_B of 10 is not necessarily overvalued. Its key assets (code, user base) are intangible and not well reflected in book value.