How do I find the weight of leftover filament?

Weigh the full spool on a kitchen scale, then subtract the empty-spool weight printed on the label.

Filament Length Calculator — Grams to Meters

Q: Why does a small diameter change matter so much?

Length scales with the inverse of the cross-sectional area, which is proportional to the diameter squared. A 0.05 mm diameter difference shifts the result by several percent.

Your inputs

Your result

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Enter your values to see the filament length

The most common reason to use this calculator is a practical one: you have a partial spool and you want to know if there's enough filament to finish your next print without a mid-job interruption — one of the most frustrating failures in 3D printing. Weighing the spool is fast and accurate. Converting grams to meters with this calculator tells you exactly where you stand before you commit to a 6-hour print.

The formula, explained step by step

This is the reverse of the weight-to-length calculation. You know the weight; you want the length.

Step 1 — Calculate the volume from weight and density:
Volume (cm³) = weight (g) ÷ density (g/cm³)
30 g of PLA (1.24 g/cm³): 30 ÷ 1.24 = 24.19 cm³
This tells you how much space the filament occupies.

Step 2 — Calculate the cross-sectional area of the filament:
Area (cm²) = π × (diameter ÷ 2)²
For 1.75 mm filament: area = π × (0.0875)² ≈ 0.02405 cm²
This is the "face" area of the cylinder — how much area each cm of filament occupies.

Step 3 — Divide volume by area to get length in cm:
Length (cm) = volume ÷ area
24.19 ÷ 0.02405 ≈ 1006 cm

Step 4 — Convert cm to meters:
1006 cm ÷ 100 = 10.06 m

The same 30 g of PETG (1.27 g/cm³) would give less length: 30 ÷ 1.27 ÷ 0.02405 ÷ 100 ≈ 9.81 m — 2.5% shorter because PETG is denser.

How to find your remaining filament weight

The key input to this calculator is the filament weight remaining on your spool. Here are three reliable ways to find it:

Method 1 — Weigh the spool (most accurate):
Place the entire spool on a kitchen scale. Note the total weight. Subtract the empty spool tare weight — this is printed on the label of most quality brands (e.g., "Empty spool: 210 g"). The difference is your remaining filament. If the empty weight isn't on the label, look it up on the manufacturer's website or weigh an empty spool of the same brand.

Method 2 — Estimate by visual inspection (rough):
A full 1 kg spool is about 2.5–3 cm thick of wound filament on the reel. Half a spool looks roughly half that, though filament winds non-linearly. Visual estimates are accurate to ±100–150 g — useful for a quick sanity check but not for precision planning.

Method 3 — Track from a known starting weight:
When you open a new spool, weigh it immediately with the spool (total weight). After each print, the slicer tells you how many grams were used. Subtract the accumulated usage from the starting weight. This is the most accurate ongoing method and works even when you don't have a scale handy during a session.

How to use this calculator

Weigh your partial spool and subtract the empty spool weight to get remaining filament grams.
Enter the filament weight in the calculator.
Set the diameter — 1.75 mm for virtually all modern consumer printers.
Set the density using the table below for your material.
Note the result in meters.
Compare to your slicer's length estimate. In PrusaSlicer, you can see filament length in meters in the print info panel (click the "i" icon). In Cura, it shows length in the bottom status bar after slicing. If remaining > needed, you're safe to start the print.

Material density quick reference

PLA — 1.24 g/cm³ → ~335 m per kg
PLA+ — 1.17–1.24 g/cm³ → ~335–355 m per kg
PETG — 1.27 g/cm³ → ~327 m per kg
ABS — 1.04 g/cm³ → ~399 m per kg
ASA — 1.07 g/cm³ → ~388 m per kg
TPU (95A) — 1.21 g/cm³ → ~343 m per kg
Nylon (PA12) — 1.14 g/cm³ → ~364 m per kg
PC — 1.20 g/cm³ → ~346 m per kg

Real-world use cases

Case 1: Checking before a long print

You have a partial spool that weighs 1,340 g total. Empty spool weight is 210 g. Remaining filament: 1,130 g of PETG. Your slicer says the next print uses 9.4 m. Calculator result: 1,130 g of 1.75 mm PETG = 1,130 ÷ 1.27 ÷ 0.02405 ÷ 100 ≈ 36.9 m. You have nearly 4× what you need — safe to proceed.

Case 2: The close call

Spool weighs 680 g. Empty spool: 210 g. Remaining: 470 g of PLA. Your slicer says the print uses 14.7 m. PLA result: 470 ÷ 1.24 ÷ 0.02405 ÷ 100 ≈ 15.76 m. You have just 1.06 m more than needed — a margin of about 7%. At this point, most experienced users would swap spools, because slicer estimates have ±5% variance and spool weight measurements have ±10–20 g error. The risk of a mid-print spool-out outweighs the few cents of leftover filament.

Case 3: Matching leftovers to a print

You have three partial spools of the same PLA color: 180 g, 140 g, and 95 g. You want to print a 38 g model. Which partial spool to use? All work, but the 95 g one (which contains about 3.19 m) is the best candidate for this print because it's the closest to being depleted — consolidating your inventory and freeing up the spool for reuse.

Understanding slicer length vs. weight

Slicers can report filament use in either grams or meters depending on configuration. Here's how to switch between them and why they differ:

In PrusaSlicer: the default display can be changed in Preferences → "Show filament length in meters." In Cura: the bottom bar shows length; enable weight display in the slice information panel. In OrcaSlicer/Bambu Studio: the slice popup shows both grams and meters natively.

If your slicer shows length in millimeters (mm), divide by 1000 to get meters. Some older versions of Cura report in mm. A 14,700 mm estimate = 14.7 m.

When to just swap the spool instead of measuring

If your visual inspection suggests less than 200 g remaining, swap to a fresh spool for any print over 2 hours. The cost of wasted filament from a failed spool-out (reprinting the whole part) almost always exceeds the ~$4 of "wasted" filament you'd preserve by finishing the old spool first. For multi-day prints, err heavily on the safe side — weigh the spool and calculate before starting.

Recommended: A kitchen scale accurate to 1 g (available for under $15) is one of the most useful tools in a 3D printer's toolkit — for checking filament remaining, verifying print weights and calibrating extrusion.

Frequently asked questions

How do I find the weight of filament remaining on a spool?

Weigh the full spool on a kitchen or postal scale. Subtract the empty spool tare weight — this is usually printed on the label (e.g., "~245 g" for an empty Bambu spool, "~200 g" for an empty Polymaker spool). If it's not on the label, search "[brand] empty spool weight" or weigh an empty spool from the same brand. The difference is remaining filament in grams.

Why does a small diameter change matter so much to the result?

Length scales inversely with the cross-sectional area, which is proportional to diameter squared. The relationship is: if diameter increases by X%, length decreases by approximately 2X%. So 1.75 mm vs. 1.85 mm is a 5.7% diameter increase, which causes about an 11% decrease in length per gram. This means poorly calibrated budget filament with ±0.1 mm tolerance can throw off length calculations by 10%+ — and also causes inconsistent extrusion in your prints.

My spool doesn't list the empty weight — what should I do?

Common empty spool weights by brand: Bambu Lab: 210–250 g depending on spool type. Polymaker: 200–220 g. Prusament: 200 g. Hatchbox: 230–250 g. eSUN: 195–210 g. Sunlu: 200–220 g. Amazon Basics / budget brands: 180–240 g. If you can find an empty spool from the same brand, weigh it. Alternatively, when you open a new spool, weigh it, note the total weight, and track filament usage from there — then when it runs out, you know the empty spool weight for future reference.

How do I know if I have enough filament for my next print?

Calculate remaining filament length with this tool. Then check your slicer's estimated filament length for the print. Leave at least 10–15% margin to account for slicer estimation error and scale measurement error. For a 14 m slicer estimate, you want at least 15.5–16 m remaining to be comfortable. If you're under 1 m of margin, swap to a fresh spool — the risk of a spool-out failure on a 6+ hour print isn't worth the small amount of filament you'd save.

Does the slicer show filament in meters or grams?

It depends on the slicer and your settings. PrusaSlicer shows weight in grams by default and can show length in meters. Cura shows length in the bottom bar after slicing (in meters or mm depending on version). OrcaSlicer and Bambu Studio show both grams and meters in the slice popup. Some slicers show millimeters — divide by 1000 to convert to meters for comparison with this calculator's output.

Is there a quick rule of thumb for common filaments?

Yes, roughly: PLA — 1 g ≈ 0.336 m (or ~3 g per meter). PETG — 1 g ≈ 0.327 m (~3.06 g/m). ABS — 1 g ≈ 0.399 m (~2.51 g/m). TPU — 1 g ≈ 0.343 m (~2.92 g/m). These quick ratios let you estimate in your head for common checks. For anything precise — especially when cutting it close — use the full calculator with your exact diameter and density values.

Why might my actual remaining length be different from the calculation?

Three main reasons: (1) Scale inaccuracy — kitchen scales can have ±5–20 g error, which translates to ±1.5–6 m error on length. (2) Density variation — filament density can vary ±3% from the nominal value, especially in budget brands. (3) Extrusion multiplier — if your printer extrudes more than commanded (e.g., multiplier of 1.05), you use slightly more filament than the slicer estimates. Calibrate your scale with a known weight for precision work.

Can wet filament give a higher weight reading?

Yes. Hygroscopic filaments — PETG, TPU, Nylon, PVA and certain PLA+ formulations — absorb atmospheric moisture. A wet 1 kg spool can weigh 1010–1030 g of which 10–30 g is absorbed water. This inflates your remaining filament estimate by 1–3%. Importantly, wet filament also prints poorly — it causes bubbling, stringing and surface defects. If your filament has been in open air for more than a few days in a humid climate, dry it before use (50–65°C for 4–8 hours in a food dehydrator or dedicated filament dryer).

Filament Length Calculator