How to use this calculator
Weigh the spool and subtract a reliable empty-spool mass. Use the filament diameter and material density from the supplier. Enter the length required by your slicer to see whether the spool is likely to cover the print.
The formula
A worked example
A 1,300 g spool with a 300 g empty weight contains 1,000 g filament. At 1.75 mm diameter and 1.24 g/cm³ density, it holds about 335.284 m. A 100 m print leaves about 235.284 m.
Assumptions & limitations
Assumes uniform, solid cylindrical filament and accurate tare and density. Moisture, labels, spool variation, and filament tolerance affect the estimate. A negative surplus means the estimated length is insufficient; leave a practical reserve.
Common questions
Is 1.24 the right density for every filament?
No. It is an example associated with a particular PLA material. Use your supplier’s specification for your product.
What if the spool weighs less than the tare?
The measurements are inconsistent. Recheck the scale and empty-spool weight before using the estimate.
Supporting reference
The method above states this calculator’s assumptions. This reference provides related definitions and technical context.
Prusa Research: filament weight and length calculator ↗Formula and worked example checked against automated test cases. About our methodology.