The question of how much filament to keep on-hand is one that bugs every FDM 3D printer user at one point or another. Most of us usually just limit our prints to how much filament we have. Or we reschedule any bigger project based on when we would buy a new spool.
There is a better way to go about this though. And that is what we will discuss here today.
Weight versus length of filament
While both weight and length are useful ways to gauge filament consumption, the simple fact that 99% of filament purchases are in terms of weight of the filament means that it is a better ballpark to use when estimating 3D printer filament usage.
Most slicers automatically calculate an estimated weight of the 3D print on the basis of the type of material (PLA, ABS, HIPS, PETG etc.) upon slicing an STL file into G-Code. Look for “sliced information” or some similar information dialog within the slicer.
For simplicity, we’ll be talking about the weight of 3D prints in PLA. If you use another type of filament as a daily driver, then simply adjust the weights given in this article according to the difference in density between your type of filament with the density of PLA.
The amount of filament you will need in general
By “general use” we mean 3D printing parts, tools and thingamabobs every now and again, but not too often, nor on a daily basis. Basically, anything short of a full-blown project.
In this case, most 3D prints would not exceed 50 grams of filament (PLA). You can easily get away with keeping 2 or 3 spools of 1KG filament on-hand. If you use a 3D printer capable of printing with 2 or 3 filaments at the same time, then your requirement would also increase accordingly.
At the very least, every user should have 1 spare spool – recommended to be a neutral color – as a fail-safe reserve.
Project-based estimation for frequent printers
If you routinely take up entire 3D printing projects, then you would go through filament much quicker than the general user. You would also probably need different materials or at least different colors on-hand to ease out your post-processing.
In this case, it is much better to stock your filaments on the basis of your running project needs.
But how exactly does one go about accounting for all the filament that a particular project would use? If you had a final STL file ready to go, then of course you could simply slice it to find out the estimated weight of the filament.
Speaking for the broad majority of tinkerers and 3D printing enthusiasts, however, reaching a final STL file isn’t something that one does on the first day of the project and is only near the final stretch that the STL is also set in stone. Of course, the answer to this problem is, we estimate!
Estimate based on prior experience
One of the easiest ways to go about estimating the amount of filament you would need is to compare it to previous projects already completed.
For example, your current project requires you to 3D print a hexagonal container of some sort. By prior experience you know that a similar sized round container would use up 76 grams of PLA filament when printed with 20% infill.
Now a hexagon has more defined edges than a round container and perhaps you’d like to use 40% infill to make it extra sturdy, so as a rough estimate we increase the expected weight of the hexagonal container by 20% and add an extra 5% to account for the difference in shape.
Increasing the 76 grams by a total of 25%, we’d get a ball-park estimate of around 95 grams. Since this 95-grams is estimated from the consumed material of the prior project, this method has the added advantage of accounting for things such as failed prints, support structures, varying levels of in-fill as well.
Approximation (order of magnitude estimation)
The more mathematically inclined readers would be familiar with this concept named after famed physicist Enrico Fermi.
A fermi approximation only considers the order of magnitude or for our purposes, weight in grams rounded to 1, 10, 100 and so on to reach a close enough estimate of the weight of the filament.
Say, for example you want to 3D print a cosplay helmet for your own head size, but are unsure exactly how much filament it would take. A good starting point would be to consider the size of the helmet in comparison to say a 10 cm3 3D printed cube at 100% in-fill with PLA.
Surely the helmet would not be only 10 cm3 or 100 cm3, and it cannot possibly be a 1000 (10,000 cm3) times the size of the cube as well. So as the only reasonable selection, we will say that the helmet would be around 100 times the size of the cube.
Since the density of PLA is 1.25 grams per cubic centimeter, our 100% in-fill cube would weigh exactly 12.5 grams. So, our helmet at an order of magnitude of 100 times more should be around the ballpark of 1250 grams at 100% in-fill. If we are printing at 20% in-fill, then it would reduce that weight to 250 grams.
Now you may be thinking; “surely such a simple guess couldn’t be accurate?”. And you’d be right. But as an estimate goes, the Fermi approximation is a great way to reach an accuracy of within one order of magnitude or one power of 10 of the actual answer. So, the actual helmet could only be 100 grams, or it could be 400 grams, but you can be sure that you wouldn’t needmore than one 1 kg spool of filament for it. And that is what we needed to estimate: How many spools of filament you would need for the project.
Problems with estimating weight based on geometric volume of the 3D print
As a pro-tip, we would recommend you steer clear of using a geometric volume as fine way to calculate weight of the 3D print.
Firstly, most 3D prints are of a unique shape and unless you are brilliant at math, their volumes would need to be estimated by simplifying the design to Minecraft-style cuboids.
You are already uncertain of the final details of the 3D print, so you’d be making multiple guesses as to the volume of the resultant cuboids. This increases the uncertainty as the complexity of the 3D print increases.
Secondly, a volumetric approach usually would fail to account for the support structures, failed prints and other technical losses that you may face, so more often than not, you would wind up under-estimating your project requirements.
Lastly, it is human nature to make conservative guesses when faced with the unknown. In terms of estimating the required filament, this would invariably mean that the person guessing the volumes of the various parts would also under-estimate.
Since not running out of filament for the duration of the project is the entire goal of the estimation, the end-result of the geometric volume approach is time spent doing nothing worthwhile in most cases. However doing so may give a better estimate on how many spools of filament to inventory over time.
How much can be 3D printed with 1 spool of filament
Since 3D printing is an additive manufacturing process there is very limited material waste involved. With a 1 KG spool of filament, you would probably 3D print ~990 grams or so of the material.
Factors that affect this of course, is the quality of the filament. If the filament keeps breaking or keeps getting jammed, this would reduce the effective amount of filament you could 3D print with.
The other factor is the age and degradation of the 3D printer itself which would lead to increased jams, more failed prints, and more process loss at the hot end.
Minimizing material waste
The biggest contributor to wasted filaments is not the hardware nor the filament, but complex 3D print design, improper filament storage or incorrect 3D printer settings is what lead to excessive waste of material.
Support structures are arguably the bigger contributors to willful wastage of materials when it comes to complex 3D prints. Support structures can be avoided by either breaking the complex design into multiple simpler units and then attaching them in post-processing, or by incorporating the support structure into the 3D print itself; grids, interlocks, beams and scaffoldings have been a part of architecture for centuries, so consider incorporating one or more of them in your next project.
Improper filament storage is perhaps one of the biggest reasons that leads newcomers to have to buy new spools frequently. Remember, proper storage of 3D printer filaments is somewhere dry, away from sunlight, properly spooled (not tangled), and preferably in an airtight container.
Failed prints are another major culprit that waste precious filament. The best way to minimize the risk of failed prints is to learn about your material and the optimal 3D printer settings with a few test prints before doing any actual 3D printing. Learning from others’ mistakes is the best way to avoid making those same mistakes yourself.
