167.64 m of 1.75 mm PLA. Length scales linearly with mass, so a half-kilogram is exactly half of the 335.28 m a full spool gives.
Nothing subtle happens to the filament at this size. What changes is everything around it.
The packaging does not halve
A 500 g plastic reel weighs 110 to 170 g empty, against 180 to 250 g for a 1 kg reel. Half the filament, but roughly two thirds of the packaging.
That makes half-kilogram spools proportionally the worst deal in shipped mass on this site's spool table. If you are ordering by post and paying by weight, two 500 g spools cost noticeably more to ship than one kilogram of the same material.
Why 500 g exists at all
Almost always because the material is expensive, awkward or both. Half-reels are the standard unit for:
- Engineering materials where a kilogram would be a serious commitment — PPA, PC blends, high-temperature grades
- Flexibles, where TPU is routinely sold in half-reels because most people work through it slowly
- Soluble supports, which are used a few grams at a time and go off if stored badly
The common thread is a material you will not get through quickly. A half-reel that stays sealed and usable beats a full one that absorbs moisture on the shelf for a year.
What 167 metres actually builds
Enough for a couple of dozen small functional parts, or a single large one. In practical terms it is the awkward size: too much for a test, not enough for a batch.
Which is the real argument for buying a full spool of anything you print regularly, and half-reels only of things you do not.
In other materials
Density does the usual work. The same 500 g of PETG is 163.68 m and the same 500 g of ABS is 197.98 m, because a lighter polymer occupies more length for the same mass. If you switch materials mid-project, the reel that looks equally full is not carrying an equal amount of printable object.
Compute the length for other materials and diameters in the length and weight converter, and see reel weights by construction in the spool weights guide.