Resin is sold by weight and used by volume
This trips up every price comparison. A bottle labelled 1 kg is not a litre. Standard photopolymer resins run around 1.10 grams per millilitre, so a kilogram is roughly 909 mL. A $38 kilo is therefore $41.80 per litre, an 11 percent difference that vanishes silently if you treat the two units as interchangeable. Slicers report resin usage in millilitres, printers meter it by volume, and the vat is filled by volume, so litres are the unit that matters. Convert the bottle price once, up front, and enter the litre figure.
Density varies less among resins than it does among filaments, but it does vary. Standard and tough resins sit near 1.10, plant-based blends a little under, flexible and filled resins a little over, and the honest range across everything on the market is about 1.05 to 1.25 g/mL. Cured resin is denser than liquid because polymerisation pulls the chains closer, which is why a printed part weighs slightly more than the liquid volume would suggest. None of that changes the money, since resin is bought and consumed volumetrically. It only matters when you are converting a per-kilogram price or checking a weight.
Support volume is not a small correction
If your slicer gives you the resin volume for the whole plate, use that and skip this section. If you only have the model volume from CAD, the supports and raft have to be added, and the allowance is larger than most people guess. A flat part sitting almost directly on the plate with light contact points might add 10 to 15 percent. A miniature angled at 30 degrees on a full raft with medium supports frequently adds 40 to 60 percent, and heavy supports on a hollow model can exceed the model volume itself. There is no formula for this because it depends on orientation, support density and how conservative your settings are. The honest approach is to slice one representative part, compare the slicer's volume to the model volume, and use that ratio for similar work.
The consumables nobody puts in the spreadsheet
Resin printing has a longer tail of small costs than filament printing, and together they are not small.
| Item | How it is consumed | What decides the per-print cost |
|---|---|---|
| IPA or wash fluid | The whole bath is replaced when it is too loaded to clean | Bath volume divided by prints per change |
| FEP or nFEP film | Clouds, stretches, eventually punctures | Cross-section of your parts and how gentle the lift settings are |
| Filters, gloves, towels | Every print, more or less | How careful you are and how much you pour back |
| LCD panel | Exposure hours | Often quoted around 2000 h for monochrome panels |
| Resin left behind | Film on the plate, drips, what soaks into towels | Handling technique, part size, vat design |
FEP life is the most variable entry on that list. A film printing small miniatures with gentle lift speeds can survive well past a hundred plates. The same film pulling a large flat cross-section off the vat can tear in a dozen. Forty prints is a placeholder, not a prediction. Track your own and replace the number.
What the failure allowance is doing
The calculation divides the plate cost by one minus the failure rate. At 12 percent that is a division by 0.88, an uplift of about 13.6 percent. The assumption is that a failed plate is a total loss: all the resin cured or contaminated, all the time spent, the vat needing a full filter and clean before the next attempt. For MSLA that assumption is closer to reality than it is for filament printing, because a plate that fails at hour three has already polymerised most of its volume, and the fragments left in the vat mean the remaining resin needs filtering whether you like it or not. It is still an assumption, and if your failures are mostly first-layer adhesion caught in the first ten minutes, this overstates the cost.
Machine depreciation is the other modelling choice. Two thousand hours is the figure commonly quoted for a monochrome LCD, and the panel is usually the first thing to go rather than the printer around it. If you would rather treat the screen as a consumable, take it out of the machine cost, put its price and expected hours into the depreciation fields on their own, and you get the same shape of answer with a clearer meaning.
A note on what this cost does not cover
Ventilation, PPE beyond gloves, waste resin disposal and the space you can no longer use for anything else are real costs of resin printing that resist being divided by a print count. So is the time spent draining, filtering and cleaning a vat, which is the part of the process most people quietly stop counting after the first month. If you are working out whether to take on paid resin work, that unglamorous half hour per plate is worth pricing honestly before you commit to a quote.
Questions people ask
How much resin does a typical miniature use?
A 32 mm scale hollowed miniature with drain holes is commonly 1 to 3 mL of model volume, plus supports and raft, so 2 to 5 mL of resin off the plate. A solid unhollowed one of the same size can be triple that. At $40 per litre, a 3 mL part is 12 cents of resin, which is why the consumables and the failure allowance dominate the answer for small parts and the resin dominates it for large ones. Print a full plate of them and the per-part number falls sharply, because the FEP wear, the wash bath share and the electricity are spread across everything on the plate.
Is water-washable resin cheaper once you skip the IPA?
On the consumables line, usually yes, because the wash bath is water and the per-print cost of that is effectively nothing. Set the IPA price to zero and see what it does to your number. The offsets are that water-washable resins often carry a price premium per litre, that the used wash water is still contaminated photopolymer and cannot go down the drain, and that many users report water-washable parts as more brittle and more prone to absorbing water over time. Whether it works out cheaper depends on how much of your cost was IPA in the first place, which for small parts is often only a few percent.
Why does the calculator add resin lost in handling?
Because the slicer number is what goes into the part, not what comes out of the bottle. Some resin stays as a film on the build plate and drips onto the paper towel, some soaks into gloves and wipes, some stays in the filter funnel, and some clings to the walls of anything you pour it through. Three millilitres per print is a rough default and it is a bigger proportion of a small print than a large one. If you meticulously drain the plate back into the vat and filter carefully, drop it. If you are printing one small part and cleaning up afterwards, three is if anything low.
Should the wash and cure station be in the depreciation?
If you bought one, yes, and the simplest way is to add its price to the printer cost so the two depreciate together over the same print hours. That is slightly wrong in that a cure station is not really worn by print hours, but the error is a few cents and the alternative is a second set of fields for a line that will never be the deciding number. What is worth separating out is the LCD panel, because it genuinely does wear by exposure hour and it is the single largest scheduled cost on an MSLA machine.