These are simple gauges for determining approximately how much filament is needed for a given object. An object of a given cubic size would require the stated length of filament. Assuming I did my math right, we have:

1/8" filament, 1mm shell, 30% infill .5" cube = .5ft 1" cube = 3ft 2" cube = 20.6ft 3" cube = 64.8ft

and

3mm filament, 1mm shell, 30% infill 12.5mm cube = .16m 25mm cube = 1m 50mm cube = 6.73m 75mm cube = 21.16m

Since ABS has a density of about 0.037 lbs/cubic inch, 5lbs works out to about 917 linear feet of 1/8" filament (seems like a lot to me - can someone with a printer confirm?). So you can use this to keep track of how much you've used. You could also use a cheap scale, but you can't print one...yet.

Edited to add: Not sure why the renders are showing mirrored text. My original files are fine, but I've uploaded mirrored files just in case.

Edited to add: Per Bophoto's suggestion, I've recalculated these for a 1mm solid shell and 30% filled interior volume and replaced the files.

1. Print (should be ok, but I don't yet have a printer, so I haven't tested it)
2. Use
3. Gloat if necessary