Filament Remaining Calculator
Weigh the spool, subtract the empty spool weight, and see how much filament is left in grams, meters, percent of the spool, and usable copies for your next sliced print.
Filament remaining (g)450
- Estimated length remaining (m)
- 150.88
- Spool remaining
- 45%
- Required with safety margin (g)
- 110
- Enough for next print?
- Yes
- Filament margin or shortfall (g)
- 340
- Complete copies available
- 4
- Remaining material value
- $9.00
Length uses the selected material density and nominal filament diameter.
The loaded filament between the spool and nozzle is not included.
How to use this calculator
- Weigh the spool as it sits now, including the remaining filament.
- Enter the empty spool weight from the manufacturer or from a matching empty spool.
- Choose the material and filament diameter printed on the spool label.
- Enter the slicer estimate and safety margin to check the next print.
- Add the full spool price if you want an estimated value for the material left.
How the remaining filament is calculated
The calculator first finds the net filament weight on the spool. If the current spool weight is W grams and the empty spool weight is T grams, the remaining filament weight is:
R = max(W - T, 0)
That weight is converted to length by using material density and the round cross section of the filament. Diameter is entered in millimeters, so the radius in centimeters is r = d / 20. Cross-sectional area is A = pi * r^2. If density is rho in grams per cubic centimeter, length in meters is:
L = R / (rho * A * 100)
The percent left compares remaining filament to the original net filament weight printed on the label:
P = min(100, 100 * R / S)
The cap keeps a tare-weight mistake from showing a spool as more than 100% full, but the result note still flags that the inputs may include clips, desiccant, adapters, RFID parts, or another source of extra weight.
Checking the next print
For a pre-print decision, the slicer estimate is not quite enough by itself. Purge lines, priming, supports, brim, scale error, and slicer rounding can all move the real number. The safety-adjusted requirement is:
Q = J * (1 + m / 100)
J is the slicer estimate in grams and m is the safety margin percent. The calculator reports "Yes" when R >= Q, the margin or shortfall as R - Q, and complete copies as floor(R / Q). If the next-print estimate is zero, those sufficiency and copy-count checks are suppressed until you enter a positive estimate.
What moves the result most
The empty spool weight matters most for the grams remaining. A 20 g tare mistake is a 20 g material mistake. Length is also sensitive to filament diameter because area grows with the square of the radius. A 2.85 mm filament has much more plastic per meter than 1.75 mm filament, so the same 100 g gives fewer meters.
What this leaves out
This is a planning estimate, not a guarantee that a long print will finish. It does not include filament already loaded between the spool and nozzle, extra purge after a material change, humidity effects, density differences between brands, diameter tolerance along the strand, or spool drag problems. For unattended jobs, leave more reserve than the calculated margin or use a runout sensor.
Worked example
Suppose a PLA spool weighs 650 g on the scale, the empty spool weighs 200 g, and the original net filament weight was 1,000 g. The remaining filament is 450 g, so the spool is 45% full.
With PLA density set to 1.24 g/cm3 and 1.75 mm filament, the radius is 0.0875 cm and the area is about 0.02405 cm2. The length estimate is 450 / (1.24 * 0.02405 * 100), or about 151 meters.
If the slicer says the next print needs 100 g and you keep a 10% safety margin, the requirement is 110 g. The spool has a 340 g margin, enough for four complete copies. At a $20 full-spool price, the material left is worth about $9.
Common questions
How do I find the empty weight of a filament spool?
The best source is the spool maker tare weight, sometimes listed on the product page or printed on the side of the spool. If you cannot find it, weigh an empty spool from the same brand and size. Generic guesses can be off by enough to change a next-print decision.
How many meters are in 100 grams of PLA?
For 1.75 mm PLA at about 1.24 g/cm3, 100 grams is roughly 33.6 meters. For 2.85 mm PLA, 100 grams is roughly 12.7 meters. The same weight makes fewer meters when the filament diameter is larger.
Does Cura or PrusaSlicer include supports in its filament estimate?
Slicer estimates usually include the toolpaths generated for the job, including supports when supports are enabled. They may not include every purge, prime, color-change, or restart behavior on your specific printer. Add a safety margin when the spool is close.
How large should my filament safety margin be?
A 5% to 10% margin is reasonable for short, familiar prints with a calibrated scale and reliable slicer estimates. Use more for long prints, abrasive materials, heavy purge routines, uncertain tare weights, or jobs you plan to leave unattended.
Why do PLA, PETG, and ABS have different lengths at the same weight?
They have different densities, so the same mass occupies a different volume. ABS is less dense than PLA, which means 100 grams of ABS is longer than 100 grams of PLA at the same diameter. Diameter still matters because thicker filament uses more volume per meter.
What should I do when the spool is slightly short for a print?
Reduce infill, walls, supports, brim, or scale only if those changes are acceptable for the part. You can also plan a filament swap, use a runout sensor, or choose a smaller job for the partial spool. Avoid starting unattended when the calculated shortfall is small.