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Filament Length Calculator

Calculate remaining filament length from spool weight and filament diameter. Enter values for instant results with step-by-step formulas.

Reviewed by Daniel Agrici, Founder & Lead Developer

Reviewed by Daniel Agrici, Founder & Lead Developer

Formula

Length = Weight / (Density x Pi x r^2)

Filament length equals the net filament weight divided by the product of material density, Pi, and the filament radius squared. Weight is in grams, density in g/cm^3, and radius in cm, giving length in cm.

Worked Examples

Example 1: Measuring Remaining PLA on a Partial Spool

Problem:A 1.75mm PLA spool weighs 1000g when new (including the spool itself). The empty spool weighs 200g, and it currently weighs 650g. How much filament remains, and how many small prints does that cover?

Solution:Net filament now = 650 - 200 = 450g\nFull spool net filament = 1000 - 200 = 800g\nDensity of PLA = 1.24 g/cm^3\nRadius = 1.75/2 = 0.875 mm = 0.0875 cm\nCross-section = Pi x 0.0875^2 = 0.024053 cm^2\nVolume now = 450 / 1.24 = 362.90 cm^3\nLength now = 362.90 / 0.024053 = 15,088.7 cm = 150.88 m = 495.03 ft\nFull-spool length = (800/1.24) / 0.024053 = 268.23 m\nRemaining % = 450 / 800 = 56.3%\nSmall prints (~15g each) = floor(450/15) = 30

Result:150.88 m remaining (495.03 ft) | 56.3% of spool | ~30 small prints, ~9 medium, ~3 large

Example 2: Comparing PETG vs ABS Filament Length per Spool

Problem:Compare the usable length of two 1.75mm, 1kg spools with 200g tare each: one PETG (density 1.27 g/cm^3), one ABS (density 1.04 g/cm^3).

Solution:Net filament: 1000 - 200 = 800g on each spool\nCross-section = Pi x 0.0875^2 = 0.024053 cm^2 (same diameter, same for both)\n\nPETG: Volume = 800 / 1.27 = 629.92 cm^3\nLength = 629.92 / 0.024053 = 26,189 cm = 261.89 m\n\nABS: Volume = 800 / 1.04 = 769.23 cm^3\nLength = 769.23 / 0.024053 = 31,981 cm = 319.81 m\n\nABS yields 57.9 m (22.1%) more length than PETG from an identical net weight, purely because it is less dense.

Result:PETG: 261.89 m ($8.40/spool value) | ABS: 319.81 m ($5.63/spool value) | ABS gives ~58 m more per spool

Example 3: Does Switching Material Change Print Time?

Problem:A print consumes 200m of 1.75mm filament at the default settings (0.4mm nozzle, 0.2mm layers, 60mm/s). Compare the print time and material cost for PLA vs. ABS.

Solution:Feed rate = (extrusion width x layer height x print speed) / filament cross-section\n= (0.4 x 0.2 x 60) / (Pi x 0.875^2 mm^2) = 4.8 / 2.405 = 2.00 mm/s\n(no density term, so this is identical for both materials)\n\nPrint time = (200 m x 1000) / (2.00 mm/s x 3600 s/hr) = 200,000 / 7,200 = 27.8 hours — same for PLA and ABS\n\nWeight used = length_cm x cross-section_cm^2 x density\n= 20,000 x 0.024053 x density\nPLA (1.24): 481.06 x 1.24 = 596.5g -> cost = 596.5 x ($20/1000) = $11.93\nABS (1.04): 481.06 x 1.04 = 500.3g -> cost = 500.3 x ($18/1000) = $9.01

Result:Print time: 27.8 hours for both | PLA uses ~597g (~$11.93) | ABS uses ~500g (~$9.01) — time is unchanged, cost is not

Frequently Asked Questions

How much filament do I actually have left on my spool right now?

Weigh the whole spool on a kitchen scale, then enter that number as \"Current Weight\" above along with your spool's empty (tare) weight and filament diameter. The calculator subtracts the tare weight to get net filament weight in grams, then converts that to length using Length = Weight / (Density x Pi x (Diameter/2)^2) in cm, cm^3, and cm respectively. For example, a spool reading 650g with a 200g empty spool and 1.75mm PLA (density 1.24 g/cm^3) has 450g of filament left, which works out to 150.88 meters (495.03 feet) — see the worked example below for every step. A scale accurate to at least 1 gram is essential; anything coarser can throw off the length estimate by several meters.

How many meters of filament are on a full 1kg spool, by material?

At the industry-standard 1.75mm diameter, a 1kg (net) spool yields approximately: PLA 335m, PETG 327m, ABS 400m, TPU 344m, Nylon 365m, ASA 389m, PC 346m, and HIPS 396m. Denser materials (PETG at 1.27 g/cm^3, Nylon at 1.14 g/cm^3) pack less length into the same weight than lighter materials like ABS (1.04 g/cm^3), because length is inversely proportional to density for a fixed weight and diameter. At 2.85mm the same 1kg spool yields roughly 2.65x less length in every material (about 126m for PLA) since the cross-sectional area is 2.65x larger. The full breakdown with cost-per-meter is in the reference table below.

Does 1.75mm vs 2.85mm filament change how much length I have left?

Yes, significantly, even for the same weight of plastic. The cross-sectional area of 2.85mm filament is about 2.65x larger than 1.75mm (pi x 1.425^2 vs pi x 0.875^2), so the same gram-for-gram weight of material produces about 2.65x less length in 2.85mm than in 1.75mm. A 1kg net PLA spool is about 335m at 1.75mm but only about 126m at 2.85mm. Filament Length Calculator applies the correct cross-section for whichever diameter you select, so switch the diameter toggle to match your actual spool label before trusting the length result.

References

Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy