How much filament is left on the spool? Weight calculator

What this is for: there is a part-used spool on the printer and you do not know whether it will last a twelve-hour print. Weigh it on a kitchen scale, subtract the weight of the empty spool and you will see straight away how many grams and metres of filament are left. Everything is calculated in your browser; nothing is sent anywhere.

You cannot judge this by eye. Filament wound neatly looks different from the same material wound loosely, and core diameters vary between manufacturers. Weight is the only reliable method. The whole trick is knowing the weight of the empty spool — and we cover that below too, because it is the part most guides simply skip.

How we calculate it — the formula

The first step is plain subtraction: filament remaining (g) = weight of spool with filament - weight of the empty spool. The second step converts grams into metres, because your slicer reports consumption in both units and it helps to be able to compare them.

Filament is a cylinder, so its mass per metre follows from its cross-sectional area and the density of the polymer: mass per metre (g) = pi × (diameter / 2)² × density, where the diameter is in millimetres and the density in g/cm³. For 1.75 mm the cross-section is 2.405 mm², which at a density of 1.24 g/cm³ gives 2.983 g per metre. Metres are then simply grams divided by that figure.

Where the densities come from, and why that caveat matters

Porima's official FDM parameter table holds thirty fields for each of twenty-five materials, but density is not one of them. It does not appear on the manufacturer's product pages either. We are not going to hide that, or quote figures we have no source for.

The values in the table below are nominal densities for the polymer family, in common use for workshop calculations. They are not measurements of a specific Porima batch, nor a manufacturer's declaration. For pure polymers the error is small, on the order of a percent. For filled materials — PLA/CF, ABS/CF, PLA Wood, PLA Stone — the density genuinely departs from that of the base polymer and the conversion to metres will carry a larger error. With those materials, trust the grams, not the metres.

Material	Nominal density	1.75 mm — g per metre	1.75 mm — metres from 1 kg	2.85 mm — g per metre
PLA and PLA variants	1.24 g/cm³	2.98 g	335 m	7.91 g
PETG	1.27 g/cm³	3.06 g	327 m	8.10 g
ABS	1.04 g/cm³	2.50 g	400 m	6.64 g
ASA	1.07 g/cm³	2.57 g	389 m	6.83 g
HIPS	1.04 g/cm³	2.50 g	400 m	6.64 g
PC/ABS	1.15 g/cm³	2.77 g	362 m	7.34 g
TPU	1.20 g/cm³	2.89 g	346 m	7.66 g
PA (nylon)	1.14 g/cm³	2.74 g	365 m	7.27 g

The densities are nominal values for the polymer family, not manufacturer data — Porima's FDM parameter table has no density field. The gram and metre columns are calculated from those densities using the formula given above. The parameters Porima does publish are in the print temperature chart. Nylon comes in several grades of differing density (PA6 about 1.14, PA12 about 1.01) — if you know yours, enter it by hand in the calculator.

The empty-spool weight — the hardest part of the job

The whole result rests on that single number, and manufacturers rarely state it. In its FDM parameter table Porima declares only the spool material: recycled plastic, for all twenty-five items. It does not give an empty-spool weight, so you will not find a sentence here along the lines of "a Porima spool weighs exactly such and such". Instead, three methods that actually work.

1. Weigh the spool once it is empty and write the result on the core with a marker. Later spools of the same type will be practically identical. This is the most accurate method, and it is free.
2. Weigh a new, unopened spool and subtract the nominal content. A 1 kg spool gross minus 1000 g gives the core weight to within a few grams.
3. Use the indicative range from the table below, but treat the result as rough.

Spool type	Indicative weight range	Note
Solid-walled plastic	approx. 200–300 g	The heaviest and the most common.
Openwork plastic	approx. 130–230 g	Wide spread depending on the cut-out pattern.
Cardboard	approx. 90–180 g	Absorbs moisture; the weight rises over time.
Wooden or plywood	approx. 200–400 g	The widest spread; weighing is essential.
Spoolless refill	0 g	You weigh the filament itself and subtract nothing.

These are indicative ranges found on the market, not manufacturer data and not a measurement of Porima spools. The only reliable method is to weigh your own empty spool.

A worked example with real numbers

You put a part-used PLA spool on the kitchen scale and see 743 g. You weighed an identical empty spool earlier and wrote 218 g on it.

• Filament remaining: 743 - 218 = 525 g
• Mass per metre for PLA 1.75 mm: pi × 0.875² × 1.24 = 2.98 g/m
• Length remaining: 525 / 2.98 = 176 m
• The planned print weighs 85 g, so there is enough for 6 pieces with 15 g to spare

Note how sensitive the result is: if the empty spool weighed 250 g instead of 218 g, you would have 493 g left, that is 165 m. Thirty-odd grams of error is eleven metres of difference. Which is why it is worth weighing once and writing it down.

Frequently asked questions

Will the calculator detect that filament has absorbed moisture?

Indirectly, and only with nylon. Absorbed water does genuinely add to the spool weight, but with PLA or PETG we are talking about fractions of a percent, so you will not see it on a kitchen scale. PA absorbs far more. If a nylon spool weighs noticeably more than it did at purchase, that is a signal to dry it, not a reason to celebrate the extra grams.

Why does the slicer show a different length from the calculator?

Because the slicer uses the density set in your material profile, and that is often left at the default of 1.24 regardless of what you are actually printing. If you want the two figures to agree, set the same density in the slicer as you used here.

Can it be worked out from the coil diameter instead of the weight?

It can, but the result is worse. The geometric method assumes perfectly even winding and knowledge of the core diameter, and in practice neither assumption holds. Weighing is faster and more accurate.

I have a spoolless refill — what do I enter?

Enter zero in the empty-spool weight field, and the weight of the refill on its own in the gross weight field.

Related tools and pages

• 3D print parameters — the full parameter table for every Porima material.
• 3D print cost calculator — once you know how much material you have, work out what it costs to use it.
• Drying filament — temperature and time — Porima's full official matrix for 25 materials.
• Tangled filament on the spool — the risk of tangling is highest at the end of a spool.
• Filament jam — the last turns near the core have the tightest radius and bind most easily.
• The printer stops extruding mid-print — sometimes it is simply the end of the spool.
• Wet filament — symptoms, drying and storing opened spools.
• Print temperature chart — Porima's official parameters for every material.