What it means
The construction is straightforward. Take revenue as the denominator, divide every cost and profit line by it, and present the result as a percentage column next to the dollar column.
What emerges is a description of the business model rather than a description of its size. This matters because dollar profits can grow while the underlying economics deteriorate.
A company can add revenue at a lower margin, report a bigger operating profit in dollars and still be getting weaker per unit of sales. The percentage column exposes that immediately, which is why investors and lenders look at it before the growth story.
In day-to-day use, the most watched lines are gross margin, sales and marketing as a share of revenue, and operating margin. Software businesses typically run high gross margins and heavy sales spend; distributors run thin gross margins and light overhead.
Knowing the normal shape for your sector turns the percentages into an early warning system. The technique also works well for internal management reporting by segment or by site.
Expressing each branch, product line or store as a common size income statement makes underperformance visible even when the units differ hugely in size. A small branch with a 45% gross margin may be worth more attention than a large one at 28%.
The nuance is that percentages depend on what sits in each line. If one company puts inbound freight in cost of goods sold and another puts it in distribution expenses, their gross margins are not comparable without adjustment.
Always check the accounting policy note before drawing conclusions from a competitor comparison.
In practice
Real-world examples.
Example
A subscription software company shows gross margin at 78% and sales and marketing at 46% of revenue. Its board accepts the heavy sales spend because customer contracts renew for several years, but sets a target to bring marketing below 40% once growth moderates.
Example
A restaurant group compares 22 sites in common size form. Food cost runs between 27% and 34% of sales, and the three worst sites share the same regional supplier, which turns a vague suspicion about waste into a specific procurement action.
Example
A packaging manufacturer's revenue rises 18% while gross margin slips from 31% to 27% of sales. Management traces the fall to a single low-priced contract won on volume, and the common size view supplies the evidence needed to reprice it at renewal.
Formula
Calculation
Common size percentage = (income statement line / revenue) x 100
A consumer electronics accessories business reports revenue of $8,000,000, cost of goods sold of $4,800,000, sales and marketing of $1,200,000, administrative expenses of $800,000 and research and development of $400,000.
Revenue = $8,000,000 / $8,000,000 = 100.0%
Cost of goods sold = $4,800,000 / $8,000,000 = 60.0%
Gross profit = $8,000,000 - $4,800,000 = $3,200,000, or 40.0% of revenue
Sales and marketing = $1,200,000 / $8,000,000 = 15.0%
Administrative expenses = $800,000 / $8,000,000 = 10.0%
Research and development = $400,000 / $8,000,000 = 5.0%
Operating profit = $3,200,000 - $1,200,000 - $800,000 - $400,000 = $800,000, which is $800,000 / $8,000,000 = 10.0% of revenue
Read as a sentence, every $1.00 of sales leaves 40 cents of gross profit, of which 30 cents is consumed by operating costs, leaving 10 cents of operating profit.Case study
Seen in the real world.
Kestrel Audio Group is an illustrative, fictional maker of headphone accessories with revenue of $8,000,000. Its monthly reporting pack showed dollar figures only, and because operating profit had risen from $700,000 two years earlier to $800,000, nobody looked further.
Restating the year in common size form told a different story. Cost of goods sold had risen to 60% of revenue from 55% two years earlier as the company shifted its mix towards a low-priced entry product, while sales and marketing had climbed to 15% of revenue to support that product. Operating profit stood at 10% of revenue against 14% two years before, so the business was working considerably harder for each extra dollar of profit.
In this fictional example the finance director rebuilt the pack around percentages of revenue by product line. The entry product was repriced and one loss-making accessory was discontinued, and within four quarters gross margin recovered to 37% without any loss in total revenue.
Watch out
Common mistakes.
- Celebrating higher dollar profit while operating margin as a share of revenue is falling.
- Comparing gross margin percentages between companies without checking which costs each one puts above the gross profit line.
- Using net revenue for some lines and gross revenue for others, which makes the percentage column internally inconsistent.
Questions
People also ask.
What is the base for a common size income statement?
Total revenue, set at 100%, with every other line divided by it.
Which lines should I watch most closely?
Gross margin, the largest operating expense category and operating margin, because those three explain most of the movement in profitability.
Can I build one for a division rather than the whole company?
Yes, and it is often more useful, because expressing each division or site as a percentage of its own revenue makes units of very different sizes directly comparable.
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