ISO 286 Tolerance and Fit Calculator (H7/g6)
Look up upper and lower deviation limits for ISO 286 holes and shafts, and compute clearance or interference for a chosen fit pair. Covers tolerance grades IT6 through IT11 for sizes up to 500 mm, the range used in the large majority of general machine design.
How to use this calculator
- Enter the nominal size in millimetres.
- Choose a hole tolerance (for example H7) and a shaft tolerance (for example g6).
- Read the limits for both members plus maximum and minimum clearance or interference.
Frequently asked questions
How is the IT tolerance value calculated?
ISO 286 derives IT grades from a standard tolerance unit i that depends on the geometric mean of the size step: IT6 = 10i, IT7 = 16i, IT8 = 25i, IT9 = 40i, IT10 = 64i and IT11 = 100i. The standard then publishes each grade rounded to a preferred value, and this calculator uses those published ISO 286-1 table values rather than the raw formula output: at the 6 to 10 mm step the formula yields IT7 = 14 um while ISO 286-1 publishes 15 um, so the table is the authority.
What does H7/g6 give me?
H7/g6 is a sliding or close running fit with a small guaranteed clearance. H7 is a hole whose lower deviation is zero, g6 is a shaft with a negative upper deviation, so the pair always has clearance.
Why use a hole-basis system?
Holes are produced with fixed-size tooling such as drills and reamers, so it is cheaper to hold the hole constant and vary the shaft, which is easy to grind or turn to any diameter.