How to use the fit mean clearance calculator
This page takes the numbers you read off a tolerance table. Enter the basic size, the lower deviation of the hole, the tolerance value of the hole grade, the upper deviation of the shaft and the tolerance value of the shaft grade. It returns the hole and shaft limits, the maximum clearance, the minimum clearance or maximum interference, the mean clearance and the clearance variation. It suits comparing what one step of grade does to the spread.
Only definitions are used. The upper deviation of the hole is its lower deviation plus the tolerance value, and the lower deviation of the shaft is its upper deviation minus the tolerance value. Maximum clearance is the upper hole deviation minus the lower shaft deviation, minimum clearance is the lower hole deviation minus the upper shaft deviation, and the variation equals the sum of the two tolerance values. Grade tolerance tables and symbols such as H7 and g6 are not confirmed in an authoritative source here, which is why the tolerance values themselves are inputs. Current as of October 2026.
Inch is the default: enter the size and every deviation in inches, as in ANSI B4.1 tables read in thousandths (0.6 thousandths = 0.0006 in), and results show inches with millimeters or micrometers in parentheses. ISO 286 fit tables are published in millimeters and micrometers, so switch the units to metric to enter those values directly; for example 30 mm H7/g6 with 0, 21, -7 and 13 micrometers gives a maximum clearance of 41.0 micrometers (0.00161 in). This is a reference aid and does not replace design work; review by a qualified engineer is required.
Frequently asked questions
No. Grade tolerance tables and the reading of zone symbols are not confirmed in an authoritative source here, so they are left out. Enter the numbers you read from your own table instead.
Subtracting the minimum clearance from the maximum leaves only the width of the hole zone plus the width of the shaft zone. Tightening either grade by one step shrinks the variation by that much.
It is the midpoint between the maximum and the minimum, so it shows which way a fit leans inside the same category. A negative value means the pairing sits on the interference side on average.