Filament calculator: how much filament is on a roll

Length and weight

Filament is sold by weight and used by length, so the two have to be converted all the time. The conversion depends on only two things: how thick the filament is, and how dense the plastic is.

A kilogram of 1.75 mm PLA is about 335 metres. The same kilogram of 2.85 mm PLA is only about 126 metres, because each metre holds more than two and a half times as much plastic. Density matters too: ABS is lighter than PLA, so a kilogram of 1.75 mm ABS is closer to 400 metres, while PETG is slightly heavier and comes in a little under PLA.

The densities in the list are the typical figures manufacturers publish. A particular brand can be a few per cent either way, and filled filaments — wood, carbon fibre, glow-in-the-dark — can differ more. If the spool’s label gives a density, type it in.

How much is left on the spool

Weighing is the reliable way. Put the spool on a kitchen scale and take off the weight of the empty spool. The empty spool is the hard part: it varies a lot between brands, from around 130 grams for a cardboard spool to 250 grams or more for a heavy plastic one. The best figure is one you have weighed yourself — keep an empty spool of each brand you buy and weigh it once.

With no scale, measure the filament instead: the diameter across the outside of the wound filament, the diameter of the hub it is wound on, and the width inside the spool. The filament fills about four fifths of that ring, and the rest is gaps between the strands. It is a rough answer, good to perhaps fifteen per cent, and it is enough to tell a nearly full spool from a nearly empty one.

Is it enough for the next print?

Your slicer shows the grams a print needs before you start it. Compare that with what is left, and leave a margin: the purge line, a failed first layer that has to be restarted, and the last metre or so that never makes it off the spool all use filament the slicer did not count.

The calculator adds ten per cent for that. If what is left is close to the line, most printers can pause for a filament change partway through — M600 on Marlin and Prusa printers — and a filament runout sensor will stop the print rather than let it run dry.

How many grams of filament are in a roll?

The weight on the label is the filament alone, not the spool. A standard roll is **1 kg** (1,000 g), and that is the size almost every price, review and slicer profile assumes. Smaller **250 g** and **500 g** rolls are sold for sample colours and specialist materials, and **2 kg**, **3 kg** and **5 kg** rolls for print farms and large parts, where the price per gram drops.

So a "1 kg roll" weighs roughly 1.13 to 1.25 kg on a scale. The difference is the empty spool, which is why the weighing method below asks for it: from about 130 g for cardboard to 250 g or more for a heavy plastic spool.

The table under the calculator gives the length of every common roll size in every common material, worked out from the same densities the calculator uses.

How much filament does a print use?

Your slicer tells you exactly, in grams and in metres, the moment it has sliced the model — it is in the summary next to the print time. That is the number to put in the last box above.

Before you slice, a rough guide: a small figurine or a bracket is 10 to 30 g, a phone stand 30 to 60 g, a three-unit Gridfinity 2×1 bin about 30 g, a helmet or a vase in the hundreds. Infill and wall count matter more than size, which is why the same model can use half as much at 10% infill as at 40%.

For a figure from the model itself, drop the STL, 3MF or G-code into the 3D printing cost calculator. It measures the volume, applies your infill and walls the way a slicer would, and gives the grams and the cost.

Over a print, an ordinary printer gets through about 7 g of PLA an hour, and a fast one — a Bambu, a Prusa MK4 or Core One, anything running Klipper — about 15 to 20 g. That puts a 1 kg roll at roughly 140 hours of printing on the first and 50 to 70 on the second.

Checking the diameter

Measure the filament with calipers in a few places along a metre of it. Good filament stays within two hundredths of a millimetre of its stated size. That small difference changes the length in a kilogram by about two per cent, which is why a slicer’s filament estimate and the length you actually get can disagree slightly.