How ink works
Bottles on the shelf, tanks in the printer, and why only a refill moves your ink stock.
Ink is the hardest thing in a print shop to track, because it lives in two places at once and moves between them in a way nothing else does. PrintERP models this literally. Once you see the model, every ink number in the system makes sense.
Ink lives in two places
| Bottles on the shelf | Tanks in the printer | |
|---|---|---|
| What it is | Sealed stock you bought | Ink loaded into a machine |
| Measured in | Bottles, and millilitres inside them | Millilitres, up to a tank capacity |
| Where you see it | Inventory and Ink | Machines and the Ink Refill tab |
| Goes down when | You refill a printer | You print |
| Goes up when | You receive a purchase order | You refill it |
Why printing does not reduce your ink stock
When you print a job, no bottle leaves your shelf — the ink comes out of the tank that was already filled. The bottle only leaves the shelf when you pour it in. PrintERP records exactly that, so your inventory count always matches what you can physically see on the shelf.
So the flow is: buy a bottle → it lands in inventory → refill a tank → millilitres move from the bottle to the machine → print → millilitres leave the tank. Three separate events, each recorded where it happens.
Turning an inventory item into tracked ink
An ink bottle starts life as an ordinary inventory item, counted in bottles. To track it by the millilitre you register it on the Ink Usage Management tab. That creates a millilitre-level ledger sitting on top of the bottle count.
- 1Open Ink and switch to the Ink Usage Management tab.
- 2Choose the inventory item that holds this ink.
- 3Enter the millilitres per bottle — 70 ml, 100 ml, whatever you buy.
- 4Name the colour and pick a swatch so it is recognisable at a glance.
- 5Enter the bottle price, and the minimum and maximum pages one bottle prints.
Colours are free text
You are not limited to Cyan, Magenta, Yellow and Black. Light Cyan, Light Magenta, White, a named Pantone — type whatever you actually stock. Common names get a sensible swatch colour automatically; anything else you can set by hand.
Page yield and cost per page
The minimum and maximum pages you entered are what let PrintERP tell you what a page costs in ink. It takes the midpoint rather than either extreme, because real yield sits somewhere between the two:
average pages = (minimum + maximum) ÷ 2ml per page = millilitres per bottle ÷ average pagescost per page = ml per page × cost per millilitre
The cost per millilitre comes from what you actually paid — the bottle price if you set one, otherwise the item's unit cost — divided by the millilitres in a bottle. It is not re-derived from the yield figures, so a bad yield estimate skews the pages-per-bottle column but never corrupts your costing.
Note
If the numbers cannot produce a positive page count, the yield columns show a dash rather than a made-up figure. Fill in the minimum and maximum pages to bring them back.
Tanks, and how a job finds the right one
Each printer in Machines can have tanks — one per colour — with a capacity in millilitres and a link to the inventory item that supplies it. That link is the join between the two worlds.
When a job starts, PrintERP looks at the product recipe to see which inks it needs, then looks at the machine running that line for a tank fed by the same inventory item. That tank is the one it draws down.
A missing link means no deduction
If a printer has no tank for an ink the recipe calls for — or the tank is not linked to the same inventory item — the job still starts, but you get a warning and no ink is drawn from that machine. Check the tank setup on the Machines page if you see one of these.
Wasted ink
When you record an error on a job, the spoiled ink is costed but not deducted. That is deliberate: the ink was already taken out of the tank when the job started, so deducting it again would double-count. What the waste record adds is the money — it raises the job's waste cost so your margin tells the truth.
PrintERP can work the ink waste out for you. If one unit uses a known number of paper pieces and a known volume of each ink, then one spoiled piece carries a known share of that ink. Tell it how many pieces were ruined and it fills in the millilitres. See Recording errors and waste.
Common questions
My tank shows less than I can see in the printer.
The tank figure is an estimate based on what has been printed. When you refill, enter the approximate millilitres actually left and PrintERP will use your reading instead of its estimate.
Why did my bottle count not go down after a refill?
A bottle only leaves inventory when its last millilitre is gone. Half a bottle poured in leaves the bottle on the books. See Partial reams and bottles.
How many inks can I track?
The Free plan tracks four. Press and Production track unlimited inks. See Plans and limits.
Can I reduce ink stock by hand?
Yes — the ink detail page has a manual consume action for ink used outside a job, such as purging or a test print.
Open Ink Usage Management
Register an ink, set its yield, and see cost per page.
Related guides
Registering an ink
Link an inventory item, set millilitres per bottle, colour, price and page yield.
Refilling a printer
Full and half refills, entering what is really left in the tank, and what leaves your stock.
Partial reams and bottles
Why a whole unit only comes off the books when its last piece is spent — and what the "is it safe to say" prompt means.