You want to know whether there is enough on the spool to finish a job. You put it on a kitchen scale, and now you need one more number: the mass of the empty reel. That number is the whole problem. It is not printed on most spools, it varies between production runs of the same product, and it is the input every "how much is left" calculation depends on.
Why this site does not have a table of brands
The obvious thing to publish is a list of manufacturers with a weight against each. This site deliberately does not, and the reason is that such a list is wrong within a year.
Reel mass is a function of construction, not of branding. A company can switch from injection-moulded plastic to cardboard between batches to cut shipping weight, change the colour of the plastic — different pigment, different mass — or run two factories with different tooling. The name on the label is stable and the object it describes is not.
So the reference here is organised by what the reel is made of:
| Construction | Empty reel | Payload |
|---|---|---|
| Cardboard 1 kg reel | 140–180 g | 1000 g |
| Injection-moulded plastic 1 kg reel | 180–250 g | 1000 g |
| Prusament 1 kg reel | 195–210 g | 1000 g |
| Cardboard 500 g reel | 90–130 g | 500 g |
| Plastic 500 g reel | 110–170 g | 500 g |
| Refill coil, no reel | 0 g | 1000 g |
Look at the reel column rather than the brand column and the useful pattern appears immediately: the plastic and cardboard classes barely overlap, and the difference between them is larger than most people's mental allowance.
What guessing costs, on a real weigh-in
A part-used PLA spool reads 812 g gross on the scale. Two assumptions about the reel, everything else identical.
Assume a moulded plastic reel at 215 g and you have 597 g of filament left — 200.16 m of 1.75 mm PLA, 59.7% of a full kilogram, and 13 more prints if your typical part uses 45 g.
Assume a cardboard reel at 160 g and the same 812 g becomes 652 g — 218.6 m, 65.2% of a kilogram, and 14 prints.
The reel figure is the only guess in that calculation, and a fifty-five gram error between a cardboard reel and a plastic one moves the answer by more than a whole print. Weigh one empty reel per brand and the spool calculator turns every later weighing into a single step.
The gap between those two answers is more than a whole print. If you are deciding whether to start a 200 g job at midnight, the wrong assumption about a reel you have never weighed is exactly the error that produces a half-finished part and a machine printing into air at four in the morning.
The one-minute habit that removes the problem
Weigh the reel when it is empty and write the number on it with a marker.
That is it. You cannot do it for the spool you are using right now, but every spool you finish from today onwards gives you a permanent, exact figure for the next time you buy that product. Within a few months you will have covered the brands you actually use, and the ranges in the table above become a fallback you rarely need.
Prusa print the reel weight on every label, which is the behaviour worth rewarding and worth asking other brands for. If yours does, use the printed figure in preference to anything here.
A refill coil deserves its own mention because it is the one case where the naive arithmetic is right: with no reel to subtract, the gross weight is the filament weight. If you find the accounting irritating, MasterSpool-style refills remove it entirely, and they cut packaging waste at the same time.
Where the remaining uncertainty lives
Even with an exact reel weight the calculation is not perfect, and it is worth knowing why.
- The payload is nominal. A "1 kg" spool is sold as a kilogram of filament and is filled to a tolerance, not to the microgram.
- Cardboard reels change mass. They absorb water from the air, so a cardboard reel weighed new and weighed after a damp winter are not the same object. See storing filament so it stays printable for why that matters beyond the arithmetic.
- Density varies by pigment. Length depends on density, and a heavily filled or heavily pigmented grade is denser than the headline figure — matte and glow PLA are the notable offenders. The mass figure stays right; the metres figure moves.
- Scales lie at the ends of their range. A kitchen scale is usually accurate enough here, but check it against a known weight once. An unopened bag of sugar or a litre of water is close enough to calibrate against, and a scale that reads several grams out at one kilogram will read several grams out on every spool you ever weigh on it.
None of that undermines the method. It means the answer is good to within a few percent, which is entirely sufficient for deciding whether to start a print.
Reading the result properly
Two figures come out of a weigh-in and they answer different questions.
Grams remaining answers "will this job fit", and it is the one to trust, because your slicer reports its estimate in grams too. Compare like with like.
Metres remaining answers "how much is physically on there", which is useful for a filament runout sensor's settings or for judging whether the last of a spool is worth keeping. It depends on the density you assumed, so it inherits any uncertainty in that figure.
When the two disagree with your intuition, the grams are the safer number. Working out how much material a job needs before you start it is the same class of problem our sister site GetTheAmount deals with in other domains, and the discipline is identical: measure the container, not just the contents.