Flow rate Calibration
Each slicer has a setting to control the overall amount of filament extruded by the printer. If the flow rate is increased, more filament will be extruded. If the flow rate is decreased, less filament will be extruded.
In Simplify3D and PrusaSlicer, this is called Extrusion Multiplier. Cura calls it Flow.
My method of determining the correct flow rate is to print a hollow, single wall cube with a specified wall thickness, then measure the actual thickness of the wall and adjust the flow rate in the slicer to suit.
Some people prefer to have multiple walls and measure them together. For example, if the extrusion width was 0.4mm with two perimeters, then you would be hoping to measure 0.8mm for the cube wall. This does introduce more variables, such as the amount of perimeter overlap, and therefore a risk of the process failing. This is why I personally prefer a single wall cube, but each to their own.
Cura
Simplify3D / PrusaSlicer
