What each infill percentage costs
What really changes in your pocket when you move that slider in the slicer, with the geometry done and no estimates.
Written by Álvaro Melgar Merenciano·
It is the setting everybody reaches for to save money: dropping infill from 20% to 15% before hitting print.
That saves 22 cents on a 50 mm part. And the same slider, pushed to 100%, makes that part 82% dearer.
Both figures come from the same table, and they explain why nearly everybody moves infill in the wrong direction.
A 50 mm cube, measured from the inside
So that nothing here is an estimate, the whole guide uses the same part: a 50 millimetre cube with 0.8 mm walls and lids, which is what you get with two perimeters and four layers at 0.2.
That cube takes up 125 cubic centimetres. The shell — walls, floor and lid — is 11.62 cm³, and the cavity inside is the remaining 113.38 cm³. Infill only decides how much of that cavity gets filled.
| Infill | Cubic centimetres | Grams |
|---|---|---|
| 0% (hollow) | 11.6 | 14.4 g |
| 10% | 23.0 | 28.5 g |
| 15% | 28.6 | 35.5 g |
| 20% | 34.3 | 42.5 g |
| 25% | 40.0 | 49.6 g |
| 40% | 57.0 | 70.6 g |
| 50% | 68.3 | 84.7 g |
| 75% | 96.7 | 119.9 g |
| 100% | 125.0 | 155.0 g |
The first number already says a lot: however empty it is, the cube never drops below 14.4 grams. That is the part of the bill this slider cannot touch.
What each percentage costs
Putting those grams into the calculator, at the 15 grams an hour pace of an ordinary part and the usual fifteen minutes of handling:
| Infill | Grams | Time | Cost | Price |
|---|---|---|---|---|
| 0% | 14.4 g | 0 h 58 | $3.45 | $5.18 |
| 15% | 35.5 g | 2 h 22 | $4.12 | $6.18 |
| 20% | 42.5 g | 2 h 50 | $4.34 | $6.51 |
| 40% | 70.6 g | 4 h 43 | $5.23 | $7.85 |
| 100% | 155.0 g | 10 h 20 | $7.89 | $11.84 |
You can open any of the three most used and play with them: at 15%, at 20% or at 100%.
The time in the table is an honest estimate, not a fact: the real one comes from your slicer when you slice. The grams, on the other hand, are pure geometry.
Doubling infill does not double the plastic
Here is the misunderstanding. Going from 20% to 40% sounds like doubling, and the plastic only multiplies by 1.66: from 42.5 to 70.6 grams.
The reason is the shell. At 20%, those fixed 14.4 grams are already a third of the total, and the percentage only acts on the other two thirds. The lower the infill, the more the immovable part weighs.
The same downwards: going from 20% to 0% does not leave the part at nothing, it leaves it at 14.4 grams, 66% less plastic. That is the most this slider can ever save you, and only by hollowing the part out completely.
So the rule is: infill moves the part of the piece you cannot see, and that part is smaller than you think.
One more perimeter costs less than five points of infill
If what you want is a part that holds, the setting next door pays better. And it can be shown with the same cube, because adding a perimeter thickens the shell and shrinks the cavity at the same time.
| Perimeters | Wall | Shell | Whole part | Cost |
|---|---|---|---|---|
| 2 | 0.8 mm | 14.4 g | 42.5 g | $4.34 |
| 3 | 1.2 mm | 21.3 g | 48.0 g | $4.52 |
| 4 | 1.6 mm | 27.9 g | 53.3 g | $4.68 |
Compare the two ways of spending the same money. A whole extra perimeter adds 5.5 grams and 18 cents. Raising infill by five points, from 20% to 25%, adds 7.0 grams and 22 cents.
In other words: the entire extra wall comes out cheaper than an infill change you can barely notice. And the material goes where it works, on the outside, instead of being spread through an interior nobody touches.
I am not giving you strength numbers, because they depend on your part, but the direction of the advice is solid and the cost is right here: if you are torn between raising infill and raising perimeters, raise perimeters.
The bigger the part, the more infill decides
Everything above is worked out on a 50 mm cube, and it is worth saying that at another size the proportions change completely. The reason is geometric: the shell grows with the surface and the cavity grows with the volume, and volume runs away much faster.
| Cube | Whole part | Shell | Shell share |
|---|---|---|---|
| 20 mm | 3.7 g | 2.2 g | 59% |
| 50 mm | 42.5 g | 14.4 g | 34% |
| 100 mm | 294.9 g | 58.6 g | 20% |
| 200 mm | 2,172.9 g | 236.2 g | 11% |
On a 20 mm part the shell is 59% of the plastic: whatever you touch, infill barely moves anything. On a 200 mm one it is 11%, and then infill decides almost the whole bill.
Out of that comes the rule that sums up the whole guide: on miniatures infill does not matter; on big parts it is the first thing to look at. And if you change the size as well, the cube law comes into play, which is in why twice as big costs four times as much.
Going below 20% barely pays
With the table in front of you, the adjustment everybody makes looks rather thin. From 20% to 15% you save 7 grams: 22 cents of cost, 5%.
For twenty-two cents you are swapping a part that holds up for one that holds up less. If the part is decorative it makes no difference; if it is going to take a screw or hold something, it is a bad trade.
And one detail finishes the argument off: on the completely hollow part, which costs $3.45, $3.00 is your fifteen minutes. That is 87%. You can leave the cube hollow and the price barely moves, because what you are paying for is not the plastic: it is the time spent taking it off and packing it, which is counted in what an hour of 3D printer time costs.
100% is the only decision that shows
At the other end things change completely. From 20% to 100%, the cube goes from 42.5 to 155 grams and from $4.34 to $7.89: 82% more.
And the time goes from 2 h 50 to over ten hours. That is the part that really hurts, because it is ten hours of machine tied up not doing anything else.
Printing at 100% has its cases — small parts that will suffer, threads, things that get machined afterwards — but it is rarely the answer to “I want it to hold”. Between 20% and 40% there is usually more gain per dollar than between 40% and 100%.
On strength I am not giving you numbers, because it depends on your part, your material and how you load it. On cost I will: every twenty-point jump above 40% costs you more than the one before, in grams and in hours.
Where it does show: in batches
Twenty-two cents a part is noise. A hundred parts is not.
| Infill | Filament | Spools | Machine hours | Cost |
|---|---|---|---|---|
| 15% | 3.5 kg | 3.9 | 237 | $412 |
| 20% | 4.3 kg | 4.7 | 284 | $434 |
| 40% | 7.1 kg | 7.8 | 471 | $523 |
| 100% | 15.5 kg | 17.2 | 1,033 | $789 |
Between 20% and 100% there are 11 kilos of filament and $355 of difference. And, above all, 749 machine hours: a whole month of printer running non-stop, just for having pushed one slider.
The spools in the table already have the 10% that goes to waste knocked off, as explained in how long a 1 kg spool lasts.
That is why infill is a production decision, not a per-part one: on one part it is not worth thinking about; on a hundred, it is the first thing to look at.
And when it fails, 100% hurts four times as much
There is a cost to high infill that shows up on no price list: what gets thrown away when the print collapses.
A failure gives no warning, and it usually arrives late, with the part well under way. This is what you lose if it goes down 80% of the way through:
| Infill | Grams binned | Hours lost | Cost of the failure |
|---|---|---|---|
| 15% | 28.4 g | 1.9 | $0.82 |
| 20% | 34.0 g | 2.3 | $0.98 |
| 40% | 56.5 g | 3.8 | $1.62 |
| 100% | 124.0 g | 8.3 | $3.56 |
The same failure costs $3.56 at 100% and 98 cents at 20%: nearly four times more. And it is eight machine hours to do again, not two.
That changes the earlier sum. Going to 100% does not just make the part 82% dearer: it also multiplies what every mishap costs you, and long prints fail more often than short ones simply because there is more time for something to happen. The causes and the yearly cost are in why 3D prints fail.
The pattern changes the time, not so much the plastic
Below the percentage there is another menu, the pattern: grid, gyroid, honeycomb, lines, cubic. And here it is worth being clear about what I know and what I do not.
What I can state: at the same percentage, the plastic is practically the same. 20% is 20% of the cavity, however it is drawn. The grams in the table above hold for any pattern.
What changes is the time, and quite a bit: patterns that print in one continuous run, without lifting the nozzle, come out faster than those that force a jump at every crossing. How much faster depends on your machine, and the one who tells you is your slicer: change the pattern, slice again and compare the time.
And since time is money — power, depreciation and a machine that is busy — that one is an adjustment that can pay. With the grams equal, the whole difference is in the hours.
What this slider does not fix
Three things sit outside infill, and it is worth knowing before you wrestle with it.
The walls. You have seen it above: for a part that holds, the perimeter pays better and costs less. Infill is not the strength setting.
The supports. They are not infill and they can weigh as much as it does. They go separately and get thrown away whole.
The size. No percentage makes up for a part twice as big: there the plastic multiplies by eight, and that is in why twice as big costs four times as much.
Do it with your own numbers
None of this has to be taken on trust: your slicer tells you in thirty seconds.
One. Slice your part at the infill you always use and write down the grams and the time.
Two. Change only the infill, slice again and write it down again. Without touching anything else.
Three. Put both pairs of numbers into the cost calculator and look at the real difference, in money.
The usual outcome is a surprise much like this guide's: far less than you expected going down, and far more than you expected going up to 100%.
Want the exact number for your own case? 3D printing cost calculator does the full sum with your filament, your electricity tariff and your printer, and leaves the quote ready to copy.
Frequently asked questions
How much does dropping infill from 20% to 15% save?
On a 50 mm cube, 7 grams: 22 cents of cost, 5%. The selling price drops by 33 cents.
It is little because the shell of the part does not change: at 20% it is already a third of the plastic, and infill only acts on the rest.
How much does printing at 100% infill cost?
The same cube goes from 42.5 to 155 grams and from $4.34 to $7.89: 82% more cost.
And from 2 h 50 to over ten hours of machine time, which on a long run is what really weighs.
Does doubling the infill double the filament bill?
No. From 20% to 40% the plastic multiplies by 1.66, not by two, because the walls and lids are the same.
The lower your starting infill, the less doubling it shows.
What is the best infill?
For cost there is no doubt: between 15% and 20% on decorative parts, and go up only if the part is going to work for a living. Between 20% and 40% is where each euro pays best.
For strength there is no single answer: it depends on your part, the material and how you load it. Raising perimeters usually pays better than raising infill.
Does the infill pattern change the price?
In plastic, almost nothing: at the same percentage the grams are practically the same with any pattern.
In time it does, and time is money. Change the pattern, slice again and compare the hours your slicer gives you.
How much does a hollow part weigh?
The 50 mm cube at 0% infill weighs 14.4 grams, against the 155 it weighs solid. That is its shell: 11.62 cm³ of wall, floor and lid.
You cannot go below that by touching infill; you would have to remove perimeters or layers, and then the part stops being solid.
How much filament do 100 parts use by infill?
A hundred cubes at 20% are 4.3 kg and 284 machine hours; at 100%, 15.5 kg and 1,033 hours.
Between those two extremes there are $355 and 749 hours of difference: on a production run, infill is the first thing to look at.
Why does my part weigh more than this table says?
Because the table is a cube and your part is another shape: the more outer surface it has for its volume, the more shell it carries and the less infill decides.
The grams that count are the ones your slicer gives you; the table is there to show which part of those grams you can actually move.
More tools and guides
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Why 3D prints fail and what it really costs youA failure halfway through costs 2.96 €, and only 32% of that is material. The four causes in order, with the real annual cost of each failure rate.
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How much electricity does a 3D printer useWork out your 3D printer's power use and what it costs per month on your own tariff. With the average wattage of the most common models.