Filament Remaining Calculator
Put the spool on a kitchen scale, pick the brand (or enter the empty spool's weight), and see exactly how many grams and meters of filament are left — and whether it's enough for the print you're about to start.
How it works
length left (m) = grams ÷ (π × (diameter ÷ 2)² × density)
Weight is the only reliable way to know what's on a spool, because you can't see how many layers are wound underneath the outer one. The single piece of information you need beyond a scale is the empty spool's weight, and that's the one most people don't have — which is why the presets exist.
Worked example
A Hatchbox PLA spool reads 640 g on the kitchen scale.
- Filament left: 640 − 225 = 415 g (about 41% of the original kilo)
- Length: 415 ÷ 2.98 g/m = 139 m
- A print needing 380 g will make it with 35 g to spare — enough, but a mid-print runout would waste 380 g, so it's worth double-checking the tare on a reel you've weighed yourself.
Empty spool weights
These are typical values compiled from manufacturer statements and community measurements. Spools change — several brands moved from plastic to cardboard between 2022 and 2025, and even the same design varies by 10–20 g batch to batch. The only exact number is the one you get by weighing an empty one.
| Spool | Approx. empty weight | Type |
|---|---|---|
| Bambu Lab reusable spool | 250 g | Plastic, two-part |
| Bambu Lab refill (core only) | 12 g | Cardboard core, no flanges |
| Prusament | 190 g | Plastic (the label often prints the exact tare) |
| Hatchbox, Inland, Elegoo, eSun (plastic) | 220 – 225 g | Standard black plastic reel |
| Creality, Sunlu | 200 – 215 g | Plastic |
| Overture, Polymaker, eSun (cardboard) | 135 – 145 g | Cardboard |
| Generic cardboard | ≈ 130 g | Cardboard |
A habit that pays off: when a spool runs out, weigh it, and write the number on the box or in a note. After a few months you'll have exact tares for every brand you buy, and the presets become unnecessary.
Turning grams into prints
Your slicer reports the grams a print needs. Compare directly with what's left, and keep a margin — the tare uncertainty alone can be ±15 g, and printers waste a little on purge lines and retractions the slicer doesn't count. If the margin is under about 10% of the print's weight, it's a gamble; either use a fresh spool, or plan to swap spools mid-print (most modern printers pause on runout, and most filaments can be spliced or simply changed at a pause).
To go the other way — how many grams a given length is, or how far 300 g will go — use the length ↔ weight converter, and to see what those grams cost, the filament cost calculator.
Frequently asked questions
How do I know how much filament is left on a spool?
Weigh the whole spool and subtract the weight of the empty spool. What's left is filament. A full 1 kg spool on a 220 g reel weighs 1,220 g; if yours reads 640 g there's 420 g of filament left. Divide by the grams-per-meter figure for the material (about 3 g/m for 1.75 mm PLA) to get the length.
How much does an empty filament spool weigh?
Between about 100 g and 260 g depending on the maker. Cardboard spools (Overture, Polymaker, eSun cardboard) are 130–150 g; standard plastic reels (Hatchbox, eSun, Inland) 210–230 g; Bambu Lab's reusable plastic spool about 250 g; Prusament about 190 g. These vary by batch, so weigh an empty one when you finish a spool and write it on the box.
How many meters are in 1 kg of filament?
About 335 m for 1.75 mm PLA, 327 m for PETG, 400 m for ABS and 344 m for TPU. For 2.85 mm filament divide by roughly 2.65. The calculator uses the density of the material you select.
Is there a way to check without weighing?
Roughly, by counting winds: measure the spool's inner and outer diameter and the width of the wound filament, but it's much less accurate than a $10 kitchen scale. Some printers (Bambu with RFID spools, Prusa with the filament counter) track usage, but only for spools they've used from new.
My scale only shows whole grams. Is that accurate enough?
Yes. One gram is a third of a meter of filament — nothing you'll notice. The bigger uncertainty is the empty spool weight, which can vary by 10–20 g between batches of the same brand.
Last reviewed September 7, 2026. Spotted an error or want another calculator? Tell us.