Digital Printing
Resolution enters squared. Doubling dpi quadruples the drops before coverage is even applied.
— mL/m2
From drop count and drop volume alone
Drop count assumes a regular grid at the stated resolution in both axes, which greyscale heads with variable drop sizes and non-square addressing do not follow exactly - the effective drop volume is image-dependent and should be calibrated by weighing ink drawn against area printed. Coverage is summed across channels and can exceed 100%. Purge share is quoted against total ink drawn and covers spitting, capping, nozzle recovery and colour changeover, but not ink lost in a head replacement. Pretreatment chemistry, which for reactive and acid inks is a substantial separate consumable, is outside this calculation, as is the steam or dry heat needed to fix the print.
Digital Textile Printing Ink Consumption, Purge Waste & Cost — free, with the formula and a worked example, at Textile School.