Understanding filament: the physics behind the calculations
All four calculators on this page share a common physical foundation: filament is a long, thin cylinder, and all the relationships between weight, length, diameter and cost follow directly from this geometry. Understanding the underlying physics helps you make better decisions — like why 2.85 mm filament gives different results than 1.75 mm, and why density matters for comparing materials.
The cylindrical filament model
Volume of a cylinder = π × r² × length, where r is the radius (diameter ÷ 2).
For 1.75 mm filament: r = 0.875 mm = 0.0875 cm. Cross-section = π × 0.0875² ≈ 0.02405 cm².
For 2.85 mm filament: r = 1.425 mm = 0.1425 cm. Cross-section = π × 0.1425² ≈ 0.06379 cm².
Notice that 2.85 mm filament has a cross-section 2.65× larger than 1.75 mm. This means for the same length, 2.85 mm filament is 2.65× heavier. Conversely, for the same weight, you get 2.65× less length in 2.85 mm filament. This is why these two standards are not interchangeable in calculations — always use the actual diameter of your filament.
How density affects every calculation
Density connects volume to weight. A denser material is heavier per cm³. For the same length of filament, a denser material weighs more:
- PLA (1.24 g/cm³) — the baseline. 1 meter of 1.75 mm PLA ≈ 2.98 g
- PETG (1.27 g/cm³) — 2.4% denser than PLA. 1 meter ≈ 3.06 g
- ABS (1.04 g/cm³) — 16% less dense than PLA. 1 meter ≈ 2.50 g. Same weight spool → more meters
- ASA (1.07 g/cm³) — similar to ABS. 1 meter ≈ 2.57 g
- TPU 95A (1.21 g/cm³) — slightly less dense than PLA. 1 meter ≈ 2.91 g
- Nylon PA12 (1.14 g/cm³) — 8% less dense than PLA. 1 meter ≈ 2.74 g
- PC (1.20 g/cm³) — 1 meter ≈ 2.89 g
- Metal-fill PLA (2.0–3.0 g/cm³) — 60–140% denser than PLA. 1 meter ≈ 4.8–7.2 g
This density difference matters for print cost too. A kilogram of ABS gives more meters (and therefore covers more print volume) than a kilogram of PETG, because ABS is less dense. To compare materials fairly on a per-print basis, use the Filament Cost per Gram Calculator rather than comparing price per kg alone.
Which calculator to use for each situation
I know the length and want to find the weight
Use the Filament Weight Calculator. This is useful when you want to know how much a length of support structure weighs for cost estimation, or when checking whether a measurement of remaining filament is sufficient for a next print.
I know the weight and want to find the length
Use the Filament Length Calculator. The most common use case: you've weighed a partial spool and want to know how many meters you have left. Compare this to your slicer's length estimate for the next print to decide if you have enough.
I want to know my material cost per print
Use the Filament Cost per Gram Calculator. Enter your spool price and weight to get cost per gram, then enter the grams for your specific print. This is also the tool for comparing different brands and spool sizes on a normalized per-gram basis.
I want to know how many of my print I can make from a spool
Use the Prints Per Spool Calculator. Essential for batch production planning — whether you're printing 20 miniatures for a tabletop game or 100 badges for a trade show.
Choosing the right filament material for your project
PLA — Start here for everything. PLA is the most beginner-friendly, available in every color, prints at low temperature (190–220°C) with no heated bed required (though a heated bed helps with adhesion). Biodegradable and low-odor. Weaknesses: low heat resistance (starts softening at ~55°C), brittle under impact. Not suitable for items that will sit in a car, near an oven, or in outdoor sun in summer.
PETG — The everyday engineering material. Higher heat resistance than PLA (~75°C), better impact resistance, food-safe options available (print without ABS or painted surfaces). More flexible than PLA, better layer adhesion. Requires slightly higher temperatures (230–250°C, 70–85°C bed). Some stringing and oozing issues. The go-to upgrade from PLA for functional parts.
ABS — The classic engineering plastic. Higher heat resistance than PETG (~100°C), paintable (acetone-smooth finish), good chemical resistance. Major drawbacks: warping without an enclosure, strong fumes (needs ventilation), poor bed adhesion without an enclosure and bed temperature of 100–110°C. Largely superseded by ASA and PETG for most applications.
ASA — The outdoor-rated ABS. UV-resistant (where ABS yellows and becomes brittle in sunlight, ASA remains stable), similar heat resistance, better moisture resistance. The correct choice for outdoor signage, automotive parts, garden equipment. Same warping challenges as ABS; requires enclosure.
TPU (flexible) — Shore hardness typically 85–98A. Used for phone cases, flexible joints, gaskets, shoe soles, grips. Requires direct drive extruder for reliable results (Bowden setups can cause jams with flex). Print slowly (20–40 mm/s). Excellent layer adhesion and impact resistance. Higher density than PLA but less material per meter compensates in applications where less material is used for the same volume.
Nylon (PA6, PA12) — Strong, tough, excellent fatigue resistance. Excellent for functional parts like gears, living hinges, snap fits, structural components. Major weakness: hygroscopic — Nylon absorbs moisture from the air and must be dried before printing (4–8 hours at 70°C) and ideally printed from a dry box. Wet Nylon prints poorly with bubbling, stringing and weak layers.
Carbon-fiber reinforced (PLA-CF, PETG-CF, PA-CF) — The addition of short carbon fiber increases stiffness (not strength) dramatically. CF-PA can be 3–4× stiffer than standard PA at similar weight. Requires hardened steel nozzles (0.4 mm brass nozzle will wear in hours). Best for stiff structural parts where flex is undesirable. More brittle than unfilled equivalents in some directions.
Filament diameter tolerance: why it matters for your calculations
All calculations on this page assume the filament is exactly the stated diameter. In practice, there's always some variation. Quality brands maintain ±0.02 mm tolerance; budget brands can be ±0.1 mm or worse.
A diameter variation of ±0.05 mm on 1.75 mm filament changes weight per meter by:
At 1.75 mm: weight/m = π × 0.0875² × 100 × 1.24 = 2.981 g/m
At 1.80 mm: weight/m = π × 0.0900² × 100 × 1.24 = 3.153 g/m (+5.8%)
At 1.70 mm: weight/m = π × 0.0850² × 100 × 1.24 = 2.816 g/m (−5.5%)
A ±0.05 mm tolerance causes a ±5.5% error in weight estimates. For most applications this is acceptable. For precision engineering (tolerance-critical assemblies, accurate weight budgeting for aerospace or performance-critical applications), measure filament diameter at multiple points with digital calipers before relying on calculated values.
Storing filament correctly to preserve it
Filament stored in open air absorbs moisture from the environment. The impact varies by material:
- PLA — relatively stable, but will develop surface issues after months of open-air storage in humid climates. Store in sealed bags with silica gel for long-term storage.
- PETG — noticeably hygroscopic. After 24–48 hours in open air in high humidity, expect stringing and surface bubbling. Dry at 65°C for 4 hours before printing if it's been out too long.
- Nylon — highly hygroscopic. Can absorb enough moisture in a few hours to ruin a print. Must be stored sealed with desiccant and ideally printed from a dry box. Dry at 70–80°C for 6–8 hours before use.
- TPU — moderately hygroscopic. Similar care to PETG.
- ABS/ASA — less hygroscopic than the above, but still benefits from sealed storage long-term.
A sealed storage container with silica gel desiccant is the minimum. A dedicated filament dryer (eSUN eBox, PrintDry, Bambu Filament Hub) that maintains a constant low-humidity environment while printing is ideal for moisture-sensitive materials. Note that wet filament weighs slightly more — the moisture affects the accuracy of weight-based calculations by 0.5–2%.