There are wonderful calibration sets around. I've just made this one to learn Freecad and to make a fast printing thing to check just perimeter extrusion width (advanced perimeter and extruder tuning).

How to

1. Slice the thing (be sure to set perimeters=1 in vertical shells) and open the gcode file.
2. Take note of perimeters extrusion width parameter. In my case it was 0.67, calculated autamatically by Slic3r for a 0.2 layer height with a 0.4mm nozzle.
3. Print.
4. Measure it. Don't include the 2 or 3 bottom layers. Measure the four walls and dismiss the more different one. Average the other three and compare with the parameter in the gcode file.
5. If it's the same, you're done. It should be the same if your extruder steps are correct and you have also measured the filament diameter and have introduced it in the slicing software. If you continue experiencing issues, some people use the extrusion multiplier to adjust this. Extrusion multiplier = Expected value / Measured value. In any case it shouldn't be outside the range 0.9 - 1.1.