The Pantone CMYK Guide has colours which have values as follows: CMYK = 0,25,56,8 The total does not add up to 100, therefore how to interpret these values into percentages?
CMYK colours rarely will add up to 100, and there is no reason they should.
Each of the numbers in CMYK (xx,xx,xx,xx) ARE percentages of coverage of each colour, Not ratios of the total.
A lot will be well under, take a very light magenta colour (light pink if you ilke) could be 00,10,00,00
Some will be over 100, take a really strong green: 50,00,100,00
When designing for print, many printers will specify a maximum - this is to negate drying issues, bleed, transfer between sheets etc...
You see, CMYK printing, (Inkjet, offset Litho, Laser etc) vary the intensity of each colour on the white page by laying down a percentage cover, this could be fine lines, small dots or other patterns - the percentage figure of each colour is basically the amount of colour vs white space in a particular area.
Pantone colours are what are known as "Spot colours" which are designed to be printed alone, not overlaid with others, and in the Pantone Formula Guides, these ink mix formulas ARE specified as percentages!
You can convert (well emulate) Pantone colours into CMYK for use in other printing processes, but accuracy may suffer.
CMYK guides are not a formula guide. CMYK percentages and CMYK process inks are not used for mixing solid colour inks.
Pantone makes a special Colour formula guide for mixing solid inks. That's what you need. See here - in fact you don't need to mix these inks at all, that's your printers job. Leave it to the professionals.
All your printer needs from you is the Pantone number.
A CMYK colour guide is a systematic display of the colours obtained from printing the four basic process colours: cyan, magenta, cyan, and black.
In use, a sample is compared to the colour patches printed in the colour guide, then after a match is found, identify clearly the combination of process colours that closely match your sample.
A good-quality colour guide is printed on the actual press used by the printer. It is a press proof. It can be printed on coated and uncoated stock so differences in coatings can be anticipated. It can be varnished and unvarnished, in addition to all the foregoing.
Each page of the guide has an arrangement of various percentages of the ink combinations arranged in rows and columns. One hue is in columns increasing by steps from 0 to solid (100%). A second hue is in rows increasing by steps from 0 to solid (100%). A third hue is printed aligned with the above grid by page increasing by increments of 10% from 0 on the first page to solid (100%) on the last page.
This 10-page colour guide contains 1000 different colours over 10 pages of 100 colours.
In this "example" colour guide, each of the patches are labeled with the C, M, and Y percentage.
Under one such patch, one might select a colour. It might be identified as C-30, M-0, Y-30. These are percentage screens (tints) of the process colours printed on a white paper stock.
This means, the colour break for the patch is 30% Cyan and 30% Yellow which is a pale green.
Meanwhile; A Pantone System Printer's Edition shows Pantone colours with a Pantone Matching System index number along with a "recipe" to mix the colour using different amounts of the proprietary Pantone "basic" colours.
In use, you could fulfill your burning desire for Pantone 393U by mixing 4 parts Pantone Yellow, ⅛ part Pantone Green, and 60 parts white and then printing a solid patch of this on uncoated paper stock.
The CMYK colour guide mixes colours by screen tints overprinted upon one another. The Pantone formula guide is a chromatically organized spot colours by ink formulations.
Can it be done like this?
Suppose the formula is C:10, M:70, Y:15, K:5. I could take a leap here and say that C:10 could be described as 10% Cyan and 90% Transparent White for the 100% needed. And so on for the rest of the formula. If there are 4-100%-mixes, then the percentage formula for each CMYK color would be:
C=10/100=2.5%, M=70/400=17.5%, Y=15/400=3.75%, K=5/400=1.25%. The rest is filled with transparent white.
Resulting in this mixing formula:
Just a theory, haven't tested it out. If you do, comment back.