Two straight lines
Offset and digital are both linear in the number of sheets. Offset has a big intercept and a shallow slope; digital has almost no intercept and a steeper one. On the numbers in the form, offset starts at 275 dollars — 128 for eight plates, 125 for fifty minutes of make-ready at 150 an hour, and 22 dollars of paper spoiled getting to colour — and then costs about 12.7 cents a sheet to run. Digital starts at 23.30 and costs 22 cents a sheet, because every sheet carries two clicks at 5.5 cents on top of the paper.
Five thousand postcards eight-up is 625 press sheets. Offset comes to 354.17, digital to 160.80. Digital wins by more than two to one, and it is not close.
Where they cross
The crossover is the difference in the intercepts divided by the difference in the slopes: 251.70 over 9.33 cents a sheet, which is 2,697 press sheets, or 21,576 finished pieces. Below that, digital; above it, offset — and the further above, the wider the gap, because offset never stops being cheaper per sheet once the plates are paid for.
Note how far that is from the default job. A five thousand piece run is nowhere near the crossover, and the shops that quote it on offset anyway are usually the ones whose digital press is busy. Run the table at the bottom of the page and the shape is obvious: at 1,250 pieces offset is 294.89 against 57.84, more than five times the price; at 50,000 it is 1,066.69 against 1,398.30, about three quarters.
The make-ready sheets
Everybody counts the plates. Fewer people count the paper that goes through the press while the pressman brings it up to colour, and on the default job that is 200 sheets at 11 cents — 22 dollars, more than a plate. On heavy coated cover stock at 40 cents a sheet it would be 80 dollars, and on a six-colour job with a longer make-ready it can be several hundred. Waste is a fixed cost of offset in exactly the way a plate is, and leaving it out flatters the offset column on every short run.
Digital has waste too, and the clicks are charged on the bad sheets as well as the good ones. It is just much less of it — fifteen sheets rather than two hundred — because there is nothing to bring up to colour.
What the crossover does not decide
Price is one input. Offset will run stock digital presses cannot feed, will hit spot colours and metallics a four-colour process cannot reach, and looks different on uncoated paper in a way that matters for some work and not at all for others. Digital will personalise every copy, will let you approve the actual printed product rather than a proof of it, and can reprint next month without paying the make-ready twice — which is worth real money on anything that changes.
When the two totals land within ten percent, ignore the arithmetic and choose on those grounds instead. And when the job splits — a long static run plus a short personalised one — running both presses beats either column, which is the answer no single crossover number can give you.
Questions people ask
At what quantity does offset become cheaper than digital?
On the numbers in the form, about 21,600 pieces — 2,697 press sheets at eight up. But that figure is entirely made of your own inputs. Halve the plate cost or the make-ready time and the crossover drops sharply; raise the click charge and it drops too. The useful output is not the number but the sensitivity, which is why the page prints the same job at six quantities.
What is a click charge?
A per-impression fee under the service contract on a digital press, covering toner and maintenance. It is charged per side per sheet, so a duplexed sheet costs two clicks, and it is charged on spoiled sheets as well as good ones. It is the reason digital has a steep per-sheet cost that does not fall with quantity the way offset does.
Why do make-ready sheets matter so much?
Because they are paper you bought and cannot sell, and they arrive before any saleable copy does. Two hundred sheets at 11 cents is 22 dollars, more than one plate on the default job; on heavy coated stock the same 200 sheets can cost more than the whole plate set. Any offset estimate that counts plates and press time but not spoiled paper is understating the fixed cost.
Does the paper price change the answer?
Only through the waste. Both presses use the same paper for the good sheets, so that cost cancels out of the comparison — but offset spoils far more of it getting up to colour, so expensive stock pushes the crossover higher and favours digital on short runs. That is the opposite of what most people assume when they specify a heavier sheet.
Should I always take the cheaper column?
No. Offset reaches spot colours, metallics, larger sheets and stocks a digital press will not feed; digital does variable data, gives you the real printed product as a proof, and reprints without a second make-ready. When the totals land within about ten percent of each other those differences decide the job, and on a run that splits into a static part and a personalised part, using both presses beats either.