How much filament is left on a spool: calculator and empty spool weights

The formula

A scale reads filament plus spool. Take the spool away and what remains is filament:

filament left (g) = scale reading − empty spool weight
percent left      = filament left / net weight of a full spool

To turn grams into length, divide by the weight of one meter, which depends on the plastic’s density and the filament diameter:

grams per meter = density (g/cm³) × π × diameter (mm)² / 4
meters left     = filament left / grams per meter

The scale reading is exact to your scale’s resolution. The empty spool weight is the number that can be wrong, so the calculator fills it from the maker’s published figure and lets you type your own.

How do you tell how much filament is left on a spool?

Weigh the whole spool on a kitchen scale and subtract the weight of the empty spool. The difference is the filament left, in grams. Take the empty weight from the maker’s figure for that exact spool type, or weigh an emptied spool of the same brand, since spools range from 80 g to over 1,000 g.

Worked example: a part-used Bambu Lab spool

These are the calculator’s defaults: 1.75 mm PLA on a Bambu Lab reusable spool, which Bambu Lab lists at 250 g.

1. Scale reading: 612 g.
2. Filament left: 612 − 250 = 362 g.
3. One meter of 1.75 mm PLA at 1.24 g/cm³ weighs 1.24 × π × 1.75² / 4 = 2.983 g.
4. Length left: 362 / 2.983 = 121.4 m.
5. Share of the original 1,000 g: 36.2%.

Worked example: checking a PETG spool against the next print

A Polymaker 1 kg cardboard spool of 1.75 mm PETG reads 389 g. The slicer says the next print needs 180 g.

1. Filament left: 389 − 140 = 249 g, or 24.9% of the spool.
2. One meter of PETG at 1.25 g/cm³ weighs 3.01 g, so 249 g is 82.8 m.
3. Spare after the print: 249 − 180 = 69 g, about 22.9 m.

Type the slicer’s gram figure into “Next print needs” and the calculator gives the same verdict. If the spool comes up short, it shows by how much. Leave some spare for purge lines and a failed first layer.

If your slicer reports meters instead of grams, the filament length to weight converter turns them into grams.

How much does an empty filament spool weigh?

The 1 kg spools in the table below weigh 140 g to 294 g empty, depending on brand and material. Within one brand, cardboard is lighter than plastic: Spectrum lists 180 g for its 1 kg cardboard spool and 260 g for its plastic one. Spools holding 2 kg or more weigh 370 g to over 1,000 g.

Empty spool weight table

Every figure comes from the maker’s own website. “Stated” means the maker gives the empty spool weight directly. “Derived” means the maker gives a full spool weight and a net weight, and the spool is the difference.

Brand and spool type	Holds	Empty spool (g)	Where the number comes from
Bambu Lab reusable spool, low temp (ABS)	1 kg	250	Stated, Bambu Lab store specification
Bambu Lab reusable spool, high temp (ABS+PC)	1 kg	250	Stated, Bambu Lab store specification
Bambu Lab cardboard spool	1 kg	not published	Weigh one empty spool
Prusament, spools made before October 2025	1 kg	193	Stated, Prusament sample spool record
Polymaker cardboard	0.5 kg	190 ± 7	Stated, Polymaker product page
Polymaker cardboard	0.75 kg	125 ± 7	Stated, Polymaker product page
Polymaker cardboard	1 kg	140 ± 7	Stated, Polymaker product page
Polymaker cardboard	2 kg	370 ± 18.5	Stated, Polymaker product page
Polymaker cardboard (Matte PLA for Production)	2.5 kg	370 ± 20	Stated, Polymaker product page
Polymaker cardboard	3 kg	425 ± 21.3	Stated, Polymaker product page
Polymaker plastic (PP)	5 kg	819 ± 30	Stated, Polymaker product page
ELEGOO cardboard	1 kg	154 ± 10	Stated, ELEGOO product specification
colorFabb plastic	750 g	about 255	Stated, colorFabb spool chart
colorFabb cardboard	750 g	about 152	Stated, colorFabb spool chart
colorFabb plastic	1 kg	about 226	Stated, colorFabb spool chart
colorFabb plastic	2.2 kg	about 600	Stated, colorFabb spool chart
colorFabb plastic	4.5 kg	about 700	Stated, colorFabb spool chart
colorFabb plastic	8 kg	about 1,050	Stated, colorFabb spool chart
Spectrum cardboard	250 g	80	Stated, Spectrum spool table
Spectrum transparent plastic	250 g	120	Stated, Spectrum spool table
Spectrum transparent plastic	500 g	240	Stated, Spectrum spool table
Spectrum transparent plastic	1 kg	260	Stated, Spectrum spool table
Spectrum cardboard	1 kg	180	Stated, Spectrum spool table
Spectrum black plastic	2 kg	600	Stated, Spectrum spool table
Spectrum cardboard	2 kg	420	Stated, Spectrum spool table
Spectrum black plastic	4.5 kg	780	Stated, Spectrum spool table
Spectrum black plastic	8 kg	1,020	Stated, Spectrum spool table
3D-Fuel	1 kg	294	Derived: 3D-Fuel weighed a full spool at 1,294 g, minus 1,000 g net
SUNLU plastic	1 kg	about 200	Stated as approximate in a SUNLU blog post

SUNLU’s product pages give 1.3 kg gross and 1 kg net. That 300 g gap also covers the box, bag and desiccant, so it overstates the spool. The blog’s 200 g figure is the better preset.

The table leaves out eSUN, Creality, Overture and Hatchbox. Their own pages give no empty spool weight or full spool weight, and a guessed number would be worse than none. For those brands and any spool not listed, weigh the first spool you empty and write the number on its side.

Why the right row matters

Every gram of error in the empty weight is a gram of error in the answer. The default reading of 612 g gives 362 g left on a Bambu Lab reusable spool. Treated as a Polymaker 1 kg cardboard spool, the same reading gives 472 g, a 110 g gap. Pick the exact brand and spool type, not the closest-looking one.

Where the maker states a tolerance, it carries straight through. Polymaker’s 1 kg spool at 140 ± 7 g means the filament left can be off by 7 g either way.

How much does an empty Bambu Lab spool weigh?

Bambu Lab lists both its reusable spools at 250 g: the white low temperature spool made of ABS and the black high temperature spool made of ABS+PC. Bambu Lab publishes no empty weight for its cardboard spools. Weigh one empty cardboard spool and reuse that figure.

Bambu Lab refills come wound on a cardboard core, and Bambu Lab’s refill guide has you clip that core into the reusable spool. Bambu Lab’s 250 g listing is for the reusable spool sold on its own, so a loaded spool also carries the core. Weigh one empty core, add it to 250 g and type the total into “Empty spool weight”.

Prusament works differently. Each spool has a QR code that opens a page with that spool’s measured data and a “What is left on my spool?” calculator. Prusa’s sample spool record lists a 193 g spool. Since October 2025, Prusament ships on a redesigned spool, so use the figure on your own spool’s page.