Filament Length Calculator
Calculate remaining filament length from spool weight and filament diameter. Enter values for instant results with step-by-step formulas.
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 1kg PLA spool (1.75mm) has a current weight of 650g. The empty spool weighs 200g. How much filament remains?
Solution: Net filament weight = 650 - 200 = 450g\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 = 0.02405 cm^2\nVolume = 450 / 1.24 = 362.9 cm^3\nLength = 362.9 / 0.02405 = 15,090 cm = 150.9 m\nOriginal: 800g filament = 268.2 m\nRemaining: 56.3%
Result: 150.9 meters remaining (495.1 feet) | 56.3% of spool | ~30 small prints
Example 2: Comparing PETG vs ABS Filament Length per Spool
Problem: Compare the total length of 1kg spools (1.75mm) of PETG (density 1.27) and ABS (density 1.04). Empty spool: 200g each.
Solution: Net filament: 1000 - 200 = 800g each\nCross-section = Pi x 0.0875^2 = 0.02405 cm^2\n\nPETG: Volume = 800/1.27 = 629.9 cm^3\nLength = 629.9/0.02405 = 26,193 cm = 261.9 m\n\nABS: Volume = 800/1.04 = 769.2 cm^3\nLength = 769.2/0.02405 = 31,987 cm = 319.9 m\n\nABS has 22% more length due to lower density
Result: PETG: 261.9 m | ABS: 319.9 m | ABS gives 58 m more per spool
Frequently Asked Questions
How do you calculate the remaining length of filament on a spool?
Calculating remaining filament length requires three measurements: the current weight of the spool with filament, the empty spool weight, and the filament diameter. First, subtract the empty spool weight from the current weight to get the net filament weight in grams. Then use the formula: Length = Weight / (Density x Pi x (Diameter/2)^2). The density depends on the filament material (PLA is 1.24 g/cm^3, PETG is 1.27 g/cm^3, ABS is 1.04 g/cm^3). For example, 500g of 1.75mm PLA has a length of: 500 / (1.24 x 3.14159 x 0.0875^2) = approximately 167.7 meters. A kitchen scale accurate to at least 1 gram is essential for reliable measurements.
What is the typical filament length on a standard 1kg spool?
A standard 1kg spool of 1.75mm PLA filament contains approximately 335 meters (1,100 feet) of filament. For 2.85mm PLA, a 1kg spool has about 126 meters (413 feet) because the thicker filament has a larger cross-section and uses more material per unit length. The exact length varies by material density: 1kg of PETG at 1.75mm yields about 327 meters, ABS gives about 400 meters (due to lower density of 1.04 g/cm^3), and TPU provides about 344 meters. Nylon at 1.75mm gives approximately 365 meters per kilogram. These differences matter when estimating how many prints you can complete with a given spool, especially for large projects.
How does filament diameter affect print quality and consumption?
The two standard filament diameters are 1.75mm and 2.85mm (sometimes labeled 3mm). The 1.75mm diameter has become the industry standard for most consumer printers because it allows more precise extrusion control, faster response to retraction commands (reducing stringing), and works with smaller, lighter extruder mechanisms. The 2.85mm filament offers more consistent flow in bowden tube setups and is preferred by some professional printers like Ultimaker. In terms of consumption, both diameters use the same weight of material for identical prints, but the 1.75mm filament feeds about 2.65 times faster through the extruder to maintain the same volumetric flow rate. Diameter consistency is critical for quality, with premium filaments maintaining tolerance within plus or minus 0.02mm.
What are the differences between common 3D printing filament materials?
PLA (Polylactic Acid) is the most popular filament, made from corn starch, easy to print at 190-220C, biodegradable, but brittle and heat-sensitive above 60C. PETG combines ease of printing with better strength and temperature resistance than PLA, printing at 220-250C. ABS is strong and heat-resistant (up to 100C) but requires an enclosed printer due to warping and fumes, printing at 230-250C. TPU is a flexible rubber-like material great for phone cases and gaskets. Nylon offers excellent strength, durability, and low friction but is hygroscopic (absorbs moisture) and difficult to print. ASA is a UV-resistant alternative to ABS for outdoor applications. Polycarbonate offers the highest heat resistance and impact strength but requires temperatures above 280C.
How do I get the most accurate result?
Enter values as precisely as possible using the correct units for each field. Check that you have selected the right unit (e.g. kilograms vs pounds, meters vs feet) before calculating. Rounding inputs early can reduce output precision.
What formula does Filament Length Calculator use?
The formula used is described in the Formula section on this page. It is based on widely accepted standards in the relevant field. If you need a specific reference or citation, the References section provides links to authoritative sources.