Filament Length Calculator
Calculate remaining filament length from spool weight and filament diameter. Enter values for instant results with step-by-step formulas.
Reviewed for accuracy by Daniel Agrici, Founder & Lead Developer
Filament Length Calculator
Calculator
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Formula: Length = Weight / (Density x Pi x r^2)
Worked example — 150.88 m remaining (495.03 ft) | 56.3% of spool | ~30 small prints, ~9 medium, ~3 large
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 Full spool net filament = 1000 - 200 = 800g Density of PLA = 1.24 g/cm^3 Radius = 1.75/2 = 0.875 mm = 0.0875 cm Cross-section = Pi x 0.0875^2 = 0.024053 cm^2 Volume now = 450 / 1.24 = 362.90 cm^3 Length now = 362.90 / 0.024053 = 15,088.7 cm = 150.88 m = 495.03 ft Full-spool length = (800/1.24) / 0.024053 = 268.23 m Remaining % = 450 / 800 = 56.3% Small 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 Cross-section = Pi x 0.0875^2 = 0.024053 cm^2 (same diameter, same for both) PETG: Volume = 800 / 1.27 = 629.92 cm^3 Length = 629.92 / 0.024053 = 26,189 cm = 261.89 m ABS: Volume = 800 / 1.04 = 769.23 cm^3 Length = 769.23 / 0.024053 = 31,981 cm = 319.81 m ABS 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 = (0.4 x 0.2 x 60) / (Pi x 0.875^2 mm^2) = 4.8 / 2.405 = 2.00 mm/s (no density term, so this is identical for both materials) Print 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 Weight used = length_cm x cross-section_cm^2 x density = 20,000 x 0.024053 x density PLA (1.24): 481.06 x 1.24 = 596.5g -> cost = 596.5 x ($20/1000) = $11.93 ABS (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.
What is the empty (tare) spool weight I should subtract, by brand?
Empty spool weight varies by manufacturer and spool design (cardboard vs. plastic vs. refillable), so always check your specific spool if precision matters. Commonly reported tare weights: Hatchbox approximately 180-200g, eSUN approximately 230-250g, Overture approximately 190-210g, and generic/no-name spools approximately 150-250g. Prusa's own refillable Prusament spool is documented at around 216g on Prusa's materials pages. If you don't know your tare weight, weigh an empty spool from the same brand once and reuse that number for every future refill — most printer communities keep running lists of measured spool weights per brand for exactly this reason.
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.
How much does 3D printing filament cost per meter or per print?
Using Filament Length Calculator's reference retail prices (roughly $18-35 per 1kg spool depending on material) and each material's yield per spool, typical cost-per-meter at 1.75mm runs from about 4.5 cents (ABS, cheap and low-density) up to about 10.1 cents (PC, expensive and high-density) — see the full per-material breakdown in the reference table below. Multiply cost-per-meter by the length a print consumes (shown in your slicer) to estimate material cost per job; add roughly 5-10% for failed prints, purges, and priming towers in real-world budgeting.
Does the filament material (PLA vs ABS vs PETG) change print time?
Not for an identical print. The feed-rate formula behind the print-time estimate — (extrusion width x layer height x print speed) / filament cross-section — has no density term, so a PLA spool and an ABS spool feeding the same length of filament into the same G-code finish in the same time. What differs between materials is weight and cost per length: for a 200m job at 1.75mm, PLA (denser at 1.24 g/cm^3) uses about 597g (~$11.93) while ABS (1.04 g/cm^3) uses about 500g (~$9.01) for the same roughly 27.8-hour print. Material choice changes your bill of materials, not your clock time.
References
Reviewed for accuracy by Daniel Agrici, Founder & Lead Developer · Editorial policy
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