How much filament does your next print actually use — in grams and dollars? This calculator turns the slicer's length estimate into real weight and real cost for any common material.
Filament Cost & Weight
Assumes solid extruded cylinder. Slicer length already accounts for infill, walls, and supports.
How to use this calculator
- Pull the filament length from your slicer (Cura: bottom-right print summary; PrusaSlicer: filament summary; Bambu Studio: preview tab). Slicer length already includes infill, walls, supports, and skirt.
- Pick your filament diameter. Most desktop printers use 1.75 mm; some Ultimakers and older machines use 2.85 mm.
- Pick the material. The density auto-fills. For exotic blends (carbon-fiber composites, metal-fills, wood-fills), pick Custom and enter the manufacturer's value.
- Enter the spool price per kilogram. If your spool is sold by total weight, divide price by weight in kg first.
Weight and cost update as you type.
The formula
Filament is an extruded cylinder. The math is straightforward:
volume (cm³) = π × (diameter_mm / 20)² × (length_m × 100)
weight (g) = volume × density
cost ($) = (weight / 1000) × price_per_kg
The /20 converts the diameter from millimeters to a radius in centimeters in one step (divide by 10 for cm, then by 2 for radius).
Worked example
A Benchy uses 5.2 m of 1.75 mm PLA. PLA density is 1.24 g/cm³. Spool cost is $22/kg.
- Radius = 1.75 / 20 = 0.0875 cm
- Length = 5.2 × 100 = 520 cm
- Volume = π × 0.0875² × 520 = 12.51 cm³
- Weight = 12.51 × 1.24 = 15.51 g
- Cost = (15.51 / 1000) × $22 = $0.34
So a Benchy costs about 34 cents in filament. A 1 kg spool prints roughly 64 Benchies.
Variable definitions
| Variable | Meaning | Typical range |
|---|---|---|
| Length | Filament fed through the extruder, in meters | 0.5 m (small parts) to 300 m+ (large prints) |
| Diameter | Nominal filament diameter | 1.75 mm or 2.85 mm |
| Density | Mass per unit volume of the polymer | 1.04 (ABS) to 1.27 g/cm³ (PETG) |
| Spool price | Cost per kilogram | $15–$50 for standard materials, $40–$120 for engineering blends |
FAQ
How do you calculate filament weight from length?
Compute cylinder volume in cm³ — π × (diameter/2)² × length — then multiply by density in g/cm³. For 1.75 mm PLA at 1.24 g/cm³, every meter weighs about 2.98 g.
What is the density of PLA filament?
PLA is 1.24 g/cm³. ABS 1.04, PETG 1.27, TPU 1.21, HIPS 1.04, ASA 1.07, Nylon ~1.13. Manufacturer values vary ±3% based on additives and pigments.
How much filament is in a 1 kg spool?
1 kg of 1.75 mm PLA holds roughly 335 m. ABS ~400 m, PETG ~327 m. Switching to 2.85 mm filament cuts length to about 38% per kilogram.
Does infill change the calculation?
No — the slicer's reported length already accounts for infill density, wall count, supports, and brim. This calculator converts that final length to weight and cost.
Why doesn't my measured weight match the calculation?
Three usual culprits: (1) actual filament diameter varies ±0.05 mm from nominal, swinging volume by ~6%; (2) density tolerances on cheap filaments can be ±5%; (3) extrusion multiplier on your printer may be miscalibrated.
Related calculators
- Stepper Motor Sizing Calculator
- 3D Print Time Estimator (coming soon)
- Layer Adhesion Strength Estimator (coming soon)
Formulas verified against Prusa Knowledge Base filament density tables and standard cylinder volume geometry. Reviewed 2026-05.
