Filament calculator

Filament is sold by weight but used by length. Slicers report one or the other, spools are labelled in kilograms, and the question in the middle of a long print is always the same: is there enough left? This filament calculator converts between grams and metres for any common filament diameter and material, shows how much one metre weighs and how many metres are on a full spool, and works out what is left on a part-used spool from its weight.

How to convert filament grams to metres

1. Choose the direction: Weight → length or Length → weight.
2. Enter the amount in grams or metres.
3. Choose the diameter (1.75, 2.85 or 3.00 mm) and the material.
4. Read the result in the dark box, with the weight per metre, the length of a 1 kg spool, the length in feet and the filament value at your spool price.

The formula

A strand of filament is a long thin cylinder. Its cross-section is π × (diameter ÷ 2)². For 1.75 mm filament that is 2.405 mm². One metre of it has a volume of 2.405 mm² × 1000 mm = 2,405 mm³, which is 2.405 cm³. Multiply by the density and you have the weight of one metre: for PLA at 1.24 g/cm³, that is 2.98 g. A 1 kg spool therefore holds 1000 ÷ 2.98 ≈ 335 metres.

The same steps work in reverse: metres × weight per metre = grams. Change the diameter and everything scales with the square of it. 2.85 mm filament has 2.65 times the cross-section of 1.75 mm, so a kilo is only about 126 metres long.

Why the material matters

Different plastics have different densities. ABS is light at about 1.04 g/cm³, so a kilogram of ABS is longer than a kilogram of PLA: around 400 metres versus 335. PETG is slightly heavier than PLA, so a kilo is a little shorter. Filled filaments like carbon-fibre PLA or wood PLA vary by brand. The material list uses typical values; if your spool label gives a density, enter it under More options as a custom density.

How much filament is left on my spool?

Weigh the spool on a kitchen scale and enter the total in grams with Weight → length. Under More options, enter the weight of the empty spool. The calculator subtracts it and shows how many grams and metres of filament are left. Empty spool weights differ by brand: cardboard spools are often around 150 to 200 grams, plastic ones 200 to 300 grams. Weigh an empty one from your favourite brand once and write it on the next spool.

Using it with your slicer

Most slicers show both filament length and weight, but some only show one, and some show length in millimetres. Use this calculator to turn the slicer's number into the one you need: grams for cost and spool planning, metres for comparing with a spool's listed length. For the cost of the whole print, including electricity and wear, use the 3D print cost calculator. To estimate the filament a model needs before slicing, try the STL volume calculator.

Spool sizes and tolerance

Most filament is sold on 1 kg spools, but 250 g and 500 g sample spools and 3 kg spools are common too. For 1.75 mm PLA at 1.24 g/cm³, one metre weighs 2.98 g, which gives:

• 250 g: about 84 m
• 500 g: about 168 m
• 1 kg: about 335 m
• 3 kg: about 1,006 m

The same 1 kg of PLA at 2.85 mm is only about 126 m, because each metre holds 2.65 times as much plastic.

Diameter tolerance changes these numbers a little. Most brands promise ±0.02 mm. A filament that is really 1.73 mm holds about 2.3% less plastic per metre than 1.75 mm, and one that is 1.77 mm about 2.3% more, so a 1 kg spool can hold anywhere from about 328 m to 343 m. That's why the calculator is a very good estimate, not an exact count. If you need to know precisely what's left, weigh the spool and subtract the empty spool weight.

Updated November 2026 · How these tools work