I printed a lot of models in last month. I spent 2 kg filament in total. I want to know how many hours have been passed while printing. As far as I read, 1 kg PLA (1.75 mm) is about 110 meters long. My default print speed is 70 mm/s. The nozzle diameter is 0.4 mm. The nozzle multiplier in the simplify3d is 0.9 .
In a very basic math, 220÷(0.7×0.04÷0.0175×0.9)=~ 153 hours.
Is this correct?
Your formula doesn't seem to take into account two important factors: layer height and average speed.
Do the math differently:
voumetric flow rate [mm^3/s] = layer height [mm] * line width [mm] * speed [mm/s]
For example, 0.2 * 0.45 * 70 = 6.3 mm^3/s
which is realistic, the extruder on the Ender 3 cannot go much faster than that reliably.
PLA weighs 1.24 g/cm^3 = 0.00124 g/mm^3
To extrude 1 kg you need 1000/(0.00124 * 6.3) = 35 hours (70 for 2 kg).
However the printer does not reach 70 mm except on straight long moves, the average speed may be lower or much lower depending on what you print.
If you print technical parts with straight edges, maybe you can multiply by 1.5 (50 hours/kg), but if you print models and small statues or similar you may need to double it (70 hours/kg).
I use Klipper as firmware and I have a macro which keeps track of printing time and filament length used.
Your math looks correct, and is also a good approximation for what I've seen in the first few weeks with my own Ender 3.
Another way to calculate (to check yourself) is to calculate the volume extruded (nozzle area times extrusion percentage times print speed -- be sure you convert everything to the same units!) in a given second, multiply by the density of your filament (common PLA runs about 1.2 g/cm^3), and get a rough figure for how long it takes to print a kilogram of filament. Your actual print time will always be higher than this approximation, because there are moves during which the extruder isn't running, infill is often set to lower extrusion level, and of course there's setup and cleanup time to account for.
