What it means
Two companies with revenue of $50 million and $500 million cannot be compared line by line in dollars. Expressed as percentages of revenue, they can: if one spends 32% on cost of sales and the other 41%, the difference is structural and worth investigating, whatever the absolute amounts.
The same company across five years, in which revenue has doubled, is equally hard to read in dollars: every cost has grown, but which have grown faster than sales? Common size analysis answers by holding the base at 100% and showing everything relative to it.
On the income statement, the base is revenue. Cost of sales, gross profit, each operating expense category, operating profit, interest, tax and net income are shown as percentages.
The result is a margin structure: gross margin, operating margin, net margin, and the cost ratios between them. Comparison with peers shows whether the company's cost structure is competitive and where it differs; comparison over time shows which ratios are moving.
A gross margin that falls from 40% to 36% over three years while selling expenses rise from 12% to 15% tells a story that the absolute figures, all rising with revenue, would not. On the balance sheet, the base is total assets.
Cash, receivables, inventory, fixed assets, intangibles and goodwill are shown as percentages of total assets; payables, debt, provisions and equity as percentages of the same total (which equals total liabilities plus equity). The result is a picture of what the company owns and how it is funded: a company with 35% of assets in receivables and another with 12% have different working capital models; a company funded 60% by debt and another 25% have different risks.
Over time, the balance sheet's common size reveals shifts: goodwill growing as a share of assets after acquisitions, inventory rising as a share while sales stagnate, equity shrinking as buybacks and losses take their toll. On the cash flow statement, the usual base is revenue, giving cash flow margins (operating cash flow, capex and free cash flow as percentages of sales), or operating cash flow, showing how the cash generated was used.
The technique's power is in what it prompts. It does not explain; it points.
A cost ratio out of line with peers demands an explanation, which may be a different business model (a company that manufactures against one that outsources), a different accounting policy (capitalising against expensing), or a genuine efficiency gap. A balance sheet structure out of line demands the same.
Analysts combine common size analysis with ratio analysis and with the notes to the accounts to move from the observation to the cause. Limitations: the analysis depends on comparable definitions and classifications (one company's "cost of sales" may include distribution, another's may not); percentages can mislead when the base is small or distorted (a year of very low revenue makes every cost ratio look terrible); and the choice of base matters (total assets for a bank means something different from total assets for a manufacturer).
Used with those cautions, it remains the fastest way to see the shape of a business.
In practice
Real-world examples.
Example
An analyst compares six airlines on fuel, labour and aircraft cost as percentages of revenue and identifies the two with structurally higher labour ratios.
Example
A lender tracks a borrower's balance sheet common size over five years and notes debt rising from 30% to 55% of total assets while equity shrinks.
Example
A company benchmarks its selling and administration ratios against an industry survey and finds its administration at 9% of sales against a median of 6%.
Think of it
“Common size analysis is like converting everyone's grades to percentages regardless of class size. A 90% is comparable whether the class has 20 or 200.
Formula
Calculation
Income statement common size: Each item / Revenue x 100%
Balance sheet common size: Each item / Total assets x 100%
Horizontal comparison: Item % in year 2 minus Item % in year 1 (percentage point change)
Worked example. Two furniture retailers and the same company across two years.
Income statements (in thousands):
Company A, year 2: revenue $120,000; cost of sales $66,000; gross profit $54,000; store costs $24,000; marketing $7,200; administration $9,600; operating profit $13,200; interest $1,800; tax $2,850; net income $8,550.
Company B, year 2: revenue $450,000; cost of sales $265,500; gross profit $184,500; store costs $76,500; marketing $36,000; administration $27,000; operating profit $45,000; interest $9,000; tax $9,000; net income $27,000.
Common size (percentage of revenue):
- Cost of sales: A 55.0%; B 59.0%
- Gross margin: A 45.0%; B 41.0%
- Store costs: A 20.0%; B 17.0%
- Marketing: A 6.0%; B 8.0%
- Administration: A 8.0%; B 6.0%
- Operating margin: A 11.0%; B 10.0%
- Interest: A 1.5%; B 2.0%
- Net margin: A 7.1%; B 6.0%
Reading: A earns a 4-point higher gross margin (premium positioning or better buying), spends 3 points more on stores (smaller, less efficient stores) and 2 points more on administration (the cost of being smaller), and 2 points less on marketing. A's operating margin is 1 point better despite being a quarter of B's size. B's higher interest ratio reflects heavier debt. The comparison directs questions: could A's store costs come down with scale; is B under-investing in gross margin by buying cheaper; is A under-marketing?
Company A, horizontal (year 1 to year 2):
- Revenue: $100,000 to $120,000
- Cost of sales: 53.0% to 55.0% (plus 2.0 points)
- Store costs: 21.0% to 20.0% (minus 1.0)
- Marketing: 5.0% to 6.0% (plus 1.0)
- Administration: 8.5% to 8.0% (minus 0.5)
- Operating margin: 12.5% to 11.0% (minus 1.5)
Reading: revenue grew 20%, but gross margin fell 2 points, more than the 1.5 points of operating leverage gained on store and administration costs; the growth was bought with lower prices or higher costs, and marketing rose. Operating profit grew from $12,500 to $13,200 (5.6%) on 20% more revenue. The common size view shows that the growth was less profitable than the headline suggests, and points at gross margin as the item to investigate.
Balance sheet, Company A, year 2 (thousands): cash $8,000 (8.9%); receivables $4,500 (5.0%); inventory $31,500 (35.0%); fixed assets $40,500 (45.0%); intangibles $5,500 (6.1%); total assets $90,000 (100%). Payables $13,500 (15.0%); debt $27,000 (30.0%); other liabilities $4,500 (5.0%); equity $45,000 (50.0%). Year 1 inventory was 30.0% of assets. The 5-point rise in inventory's share, alongside the fall in gross margin, suggests stock that had to be discounted, and inventory days confirm it.Case study
Seen in the real world.
A private equity firm reviewed a chain of pharmacies whose profit had grown steadily and whose management presented five years of rising revenue and operating profit in dollars. The firm's analyst restated the figures as percentages of revenue. Gross margin had fallen from 31% to 26% over the period as the chain's sales mix shifted from high-margin front-of-store goods to low-margin prescriptions; staff costs had fallen from 14% to 11% as the chain cut hours; and operating margin had held at 6% only because the staff cuts had offset the margin decline.
The balance sheet common size showed inventory rising from 22% to 29% of assets and payables from 18% to 27%, meaning the chain was funding stock by stretching suppliers. None of this was visible in the dollar figures, all of which had risen.
The firm's offer was structured around a plan to restore the front-of-store mix and to fund the working capital that suppliers were being made to carry, at a price 20% below management's expectation. Management's response, after the initial disappointment, was that they had watched the dollars for five years and never once looked at the percentages.
Watch out
Common mistakes.
- Comparing common size figures across companies without checking that line items are defined and classified the same way.
- Reading a percentage change as a problem without considering the base. A cost ratio rises when revenue falls even if the cost is unchanged.
- Stopping at the observation. Common size analysis points to differences; the notes, ratios and management explain them.
Questions
People also ask.
What base should be used?
Revenue for the income statement, total assets for the balance sheet, revenue or operating cash flow for the cash flow statement. Other bases (total costs, total equity) are used for specific purposes and should be stated.
What is the difference between vertical and horizontal common size analysis?
Vertical expresses each item as a percentage of a base within one period, comparing structure. Horizontal tracks each item's percentage across periods, comparing trend. Both are usually presented together.
How does common size analysis relate to ratio analysis?
Common size percentages are themselves ratios (margins, asset composition, funding mix). Ratio analysis adds relationships between statements (turnover, returns, coverage) that common size analysis alone does not show.
From the founder's library
Take it further with the book.
Build your financial confidence beyond this definition. Shihan's full-length guide, Accounting Fundamentals, takes the same plain-English approach and turns it into a complete, practical playbook for non-finance managers, business owners and students - with chapter-end quiz answers and presentation slides included.
25% off with code MMHQ25, applied at checkout. Priced in USD - checkout may show the equivalent in your local currency.
View the book and save 25%