How the print time estimate works
An FDM printer builds a part by laying down a thin bead of plastic. The volume of plastic it can put down each second is the bead's cross-section times its speed. Divide the total plastic volume by that rate and you get the time spent extruding. Real printers also slow down for corners, travel between islands, change layers and run slower outer walls, so an efficiency factor accounts for that lost time.
time (s) = volume (mm³) / (layer height × line width × speed × efficiency)
Layer height and line width are in millimeters, speed in millimeters per second, and efficiency is a fraction such as 0.5. The bottom part of the formula, without efficiency, is your volumetric flow rate in mm³/s.
Why your slicer is more accurate
This is a rough estimate. The slicer knows the actual toolpaths: how many perimeters, infill pattern, how many small features force minimum layer time, where travel happens and what acceleration your printer uses. Its estimate is usually within 5 to 15% on modern firmware with matching settings. Use this calculator for quick comparisons and quoting before you have a sliced file, and trust the slicer for the real number.
Volumetric flow limits
Speed alone is misleading because the hotend can only melt plastic so fast. If the speed you set asks for more flow than the hotend can deliver, the printer either under-extrudes or the slicer caps speed. Approximate limits for PLA:
| Hotend type | Typical max flow (PLA) |
|---|---|
| Standard brass nozzle, short melt zone | 10–15 mm³/s |
| Volcano-style long melt zone | 20–30 mm³/s |
| High-flow hotends and nozzles | 25–35+ mm³/s |
PETG, ABS and TPU usually run lower than PLA in the same hotend; TPU often much lower. If layer height × line width × speed is above your hotend's limit, the real rate is the limit, not your speed setting.
Choosing an efficiency factor
Efficiency is the share of print time actually spent extruding at the set speed. Acceleration means short moves never reach full speed, travel moves extrude nothing, and perimeters, small layers and bridges run slower. For most parts, 40 to 60% is realistic. Large, simple parts with long straight infill sit near the top. Small, detailed parts, many separate islands or low acceleration push it toward 30%.
Measuring the inputs
Use the part's plastic volume, not its bounding box. The slicer or CAD tool will report part volume, but remember infill: a 100 cm³ solid at 20% infill with three walls might only use 35 to 50 cm³ of plastic. If you know the filament weight, volume in cm³ is grams divided by density, so 125 g of PLA is about 100 cm³.
Worked example
A part uses 50 cm³ of PLA, which is 50,000 mm³. Layer height is 0.2 mm, line width 0.45 mm, speed 60 mm/s, efficiency 50%.
- Volumetric flow: 0.2 × 0.45 × 60 = 5.4 mm³/s, well under a standard hotend's limit.
- Effective rate: 5.4 × 0.5 = 2.7 mm³/s
- Time: 50,000 / 2.7 ≈ 18,500 s, or about 5.1 hours
Raising speed to 200 mm/s would ask for 18 mm³/s. A standard brass hotend could not keep up, so real time would not drop as much as the speed change suggests.
Common mistakes
- Using bounding box volume. It ignores infill and hollow areas and overstates time.
- Ignoring flow limits. Doubling speed past the hotend limit does not halve print time.
- Efficiency of 100%. No real print achieves it; results will be far too short.
- Forgetting heat-up and leveling. Add several minutes for preheating, probing and purge.
Practical tips
- Thicker layers cut time almost proportionally; 0.28 mm prints about 30% faster than 0.2 mm.
- Wider infill lines move more plastic per pass with little quality cost.
- Compare your estimate with a few real prints and adjust efficiency to match your printer.
Multiple copies on one plate deserve a note. Printing six parts at once takes less than six times as long as one, because heating, probing and cooldown happen only once, but travel between parts lowers efficiency. Use the combined volume and drop the efficiency factor by around five to ten points for busy plates.