A "standard" clearance value does not exist
Printed clearance depends on your printer's extrusion width, your slicer's horizontal expansion setting, your material's shrinkage behavior, and even the specific orientation the parts are printed in. Two printers running the same nominal settings can produce measurably different actual clearances for the same CAD gap. That is why the honest starting point is an exploratory range rather than a single number, with a real calibration measurement always taking priority once you have one.
How the planner works
If you supply a measured allowance from a calibration test on your own printer, the planner uses it directly to compute both sides of the fit. If you have not measured one yet, it falls back to a labeled exploratory range for your chosen material, drawn from widely reproduced community calibration figures, and recommends printing a small test coupon before committing the full assembly. Either way, the output is a CAD-gap planning dimension, sized for the hole/female side and the shaft/male side of the fit, not a guaranteed tolerance.
Worked example
A 20 mm sliding shaft in PLA with a measured 0.18 mm calibration allowance: the tool returns a hole-side planning dimension near 20.18 mm and a shaft-side dimension near 19.82 mm, labeled explicitly as using your calibrated value rather than a generic range, since a real measurement from your own printer is more reliable than any published figure.
Sliding versus rotating versus static fits
The assembly type you pick changes which side of the exploratory range makes sense even before you print anything. A rotating fit that binds is usually a worse outcome than one that spins a little loose, since a bound rotating joint can gall the plastic or strip a motor mount trying to force it, so a rotating assembly generally leans toward the looser end of the range. A static fit meant to be glued or fastened afterward is more forgiving of a slightly tight gap, since a snug fit before bonding often makes the final joint stronger rather than weaker.
Limitations
This tool outputs a planning gap for your CAD model, not a manufacturing tolerance guarantee. Orientation, layer lines, and any warping at the first layer can all shift the real result away from the plan, even with a good allowance value. Confirm fit on a printed test piece, especially for an assembly where a rattle, a bind, or a leak would actually matter.