How Many Metres Are in 1 kg of 3D Printer Filament?

A typical 1 kg spool of 1.75 mm PLA contains about 335 metres of filament. That is a useful rule of thumb, not a universal spool specification. The exact length depends on the filament diameter and the density of the material.

Keep grams, millimeters and cubic millimeters consistent throughout the calculation.

Worked length calculation

For 1.75 mm filament, cross-sectional area is π × (1.75 / 2)² ≈ 2.405 mm². If the material density is 1.24 g/cm³, convert it to 0.00124 g/mm³. One kilogram then represents about 1000 / (2.405 × 0.00124) ≈ 335,600 mm, or roughly 336 m. This is an estimate based on nominal diameter and density, not a guaranteed spool length.

Repeating the calculation for 2.85 mm filament gives an area of about 6.38 mm² and roughly 126 m at the same density. Diameter therefore changes length quadratically; do not scale a 1.75 mm reference linearly. Use the material supplier's documented density when available and weigh the usable filament if the remaining amount matters.

Account for spool and measurement uncertainty

A scale reading that includes the reel must subtract a known empty-spool mass, which varies by spool design. Filament diameter also varies around its nominal value, and blends or filled materials can differ in density. Treat calculated length as inventory planning. For a print decision, prefer the slicer's mass or length estimate plus a sensible reserve for purge, priming and failed starts.

State diameter and density

Length follows mass divided by density and filament cross-sectional area. A 1 kg spool therefore has different length for 1.75 mm and 2.85 mm filament, and for materials with different density. Treat a label's nominal mass and diameter as inputs, then measure remaining filament or use the slicer for a specific print.

If you have a number from a slicer or spool label and need the other unit, use InspectMesh’s Filament Length Calculator. It converts between grams and metres with your chosen diameter and material density, entirely in your browser.

Why a 1 kg spool does not always have the same length

Spool weight measures mass, while length measures how far the filament runs. A filament strand is effectively a long cylinder. A wider cylinder contains more material in every metre, and a denser material weighs more for the same length.

This means two 1 kg spools can have different stated lengths even when they are both intended for the same printer. The most important factors are:

• filament diameter, commonly 1.75 mm or 2.85 mm;
• material density, which differs between PLA, PETG, ABS and TPU;
• the manufacturer’s diameter tolerance and the actual formulation.

Filled, carbon-fibre, glow and other speciality filaments can differ more from a generic material density. When a spool label gives both weight and length, use the manufacturer’s figures for that spool.

Typical 1 kg spool lengths

The following values use common approximate material densities. They are planning figures, rounded to the nearest metre.

The wider 2.85 mm filament is not less efficient. It simply has a larger cross-section, so the same kilogram is spread over fewer metres.

How to convert filament grams to metres

The calculation uses the volume of a cylinder. First, divide the filament weight by its density to find volume. Then divide that volume by the filament’s cross-sectional area to find length.

For a 1 kg spool of 1.75 mm PLA at approximately 1.24 g/cm³, the result is about 335 m. Reversing the calculation converts a slicer’s length estimate back into grams.

You do not need to calculate this by hand for ordinary use. Enter the value you know in the Filament Length Calculator, choose the spool diameter and material, and it will provide the matching estimate.

When grams are more useful than metres

Grams are usually the clearer unit for cost and remaining-stock decisions. Material cost is based on the fraction of a spool’s weight that a print uses, regardless of filament diameter. If a slicer estimates 80 g from a 1,000 g spool, that print uses eight percent of the spool.

For a fuller estimate that includes electricity, printer time, labour and a failure allowance, use the 3D Print Cost Calculator. If you are trying to estimate material use for a particular model, read how much filament a 3D print uses first. Your slicer remains the best source for a final print estimate because it accounts for infill, walls, supports and purge material.

Check a spool without a length label

1. Read the filament diameter on the spool or printer specification.
2. Choose the closest material-density preset or use the manufacturer’s density.
3. Weigh the remaining filament if you need a stock estimate.
4. Convert the remaining grams to metres with the calculator.
5. Keep a margin for purge material, supports and a possible reprint.

A kitchen scale cannot separate the reel weight from filament weight unless you know the empty reel’s mass. Treat any remaining-length result as an estimate and avoid planning a long print too close to the calculated limit.