Short answer
Total ink coverage (the tone value sum, or TAC) is the sum of the four ink percentages at the darkest point of a file — at most 400 %. Presses and papers can only take so much wet ink before it smears, fails to dry or sets off, so each printing condition has a limit: ISO 12647-2:2013 says coated sheet-fed offset should stay under 330 % (never above 350 %), other papers lower, and newspaper coldset should stay at or below 220 %, 240 % at most.
Each pixel of a CMYK file has four tone values from 0 to 100 %. Their sum is the tone value sum; the maximum across the file is what printers mean by total area coverage or TAC. A neutral shadow in a photograph separated with little black generation might be 85/75/75/80 — 315 %. The same shadow separated with heavy black generation might be 60/45/45/95 — 245 % — and look almost the same. The limit is set in the output profile when the file is separated, which is why it cannot be fixed by editing curves afterwards without changing colour.
Ink is transferred wet, one colour on top of another within fractions of a second on a multi-colour press. Beyond a certain film thickness the later inks do not trap well on the earlier ones, the stack takes too long to dry, and ink transfers onto the back of the next sheet in the pile (set-off). Absorbent papers accept less before the image goes muddy; newsprint in coldset printing never truly dries but partly soaks in, so thin papers show through and rub off. Beyond the physical problems, extra ink adds almost nothing: above the limit shadows get no darker, only more expensive and more fragile.
The table gives the limits stated in the standards and in WAN-IFRA's guide to the newspaper standard. They are ceilings, not targets: the ECI publishes both 330 % and 300 % versions of its coated profiles, and many printers ask for less than the maximum on fast-drying or double-sided work. Digital presses, flexo and gravure have their own limits, set by the equipment maker or the printer rather than a single ISO figure, so the only reliable number for a given job is the one the printer supplies with its profile.
Separate images with the printer's profile, which enforces the limit. Watch for elements that bypass it: rich black swatches built by hand, registration colour used in artwork, placed CMYK images separated for a different process, and transparency or drop-shadow effects that stack a shadow over a rich black. Preflight tools report the maximum tone value sum; a separations preview can highlight areas over a set value. For newspapers, remember the lower limit applies to adverts supplied as CMYK — a magazine-ready file will usually exceed it.
| Process and paper | Should be below | Must not exceed | Source |
|---|---|---|---|
| Sheet-fed offset, coated | 330 % | 350 % | ISO 12647-2:2013 |
| Heat-set web offset, coated | 300 % | 300 % | ISO 12647-2:2013 |
| Sheet-fed offset, other papers | 300 % | 300 % | ISO 12647-2:2013 |
| Heat-set web offset, other papers | 270 % | 270 % | ISO 12647-2:2013 |
| Coldset newspaper on newsprint | 220 % | 240 % | WAN-IFRA guide to ISO 12647-3:2013 |
Why: The advert was separated for coated offset at 300 %+ total ink.
Fix: Re-separate with the newspaper's profile so shadows stay within 220–240 %.
Why: A transparency effect or drop shadow stacked over a rich black.
Fix: Flatten against the correct profile or rebuild the shadow to avoid ink stacking.
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
StandardStrong evidence
ISO 12647-2:2013 says the tone value sum on coated substrates should be less than 330 % and shall not exceed 350 % for sheet-fed offset, and should not exceed 300 % for heat-set web; for other substrates the limits are 300 % sheet-fed and 270 % heat-set web.
Source: ISO 12647-2:2013 Graphic technology — Process control … — Part 2: Offset lithographic processes
StandardModerate evidence
WAN-IFRA's guide to ISO 12647-3:2013 gives a total ink coverage for newspaper coldset that should not exceed 220 %, with 240 % as the maximum, down from 240 % in the earlier edition, and a minimum of 90 % black where coverage approaches the limit.
Caveat: Taken from the trade body's summary of the standard rather than the standard text.
Source: ISO 12647-3:2013 — quality standard for newspaper production; ISO 12647-3:2013 … — Part 3: Coldset offset lithography on newsprint
FactStrong evidence
ISO 12647-2:2013 notes that high tone value sums can cause poor ink trapping, back transfer and set-off because of insufficient drying.
Source: ISO 12647-2:2013 Graphic technology — Process control … — Part 2: Offset lithographic processes
FactModerate evidence
The ECI publishes both 330 % and 300 % ink-limited coated offset profiles built from the same Fogra data.
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.