Free Engineering Calculator
ISO Fit Calculator: Shaft and Hole Tolerances
An ISO fit pairs a hole tolerance (capital letter) with a shaft tolerance (lower case). H7/g6 is a sliding clearance fit, H7/h6 a locational clearance fit, H7/n6 a transition fit and H7/p6 a press fit. Enter the nominal size and pick both grades below for the limits and the resulting clearance or interference.
99.9%
Accuracy Rate
24/7
Global Ops
200+
Containers/Yr
Calculators & Converters
The Basis of Mechanical Fit
Mechanical assemblies rely on the precise relationship between a shaft and its corresponding hole. Whether a part needs to spin freely, slide under pressure, or be permanently pressed together, standardized tolerances are the only way to ensure parts from different manufacturers work together. The “Limits and Fits” system categorizes these relationships into specific classes, allowing engineers to specify the exact amount of clearance or interference required for a joint.
By selecting the correct fundamental deviation and IT (International Tolerance) grade, you can control assembly costs and performance. Tighter tolerances increase manufacturing expense, while looser tolerances can lead to excessive vibration or premature wear. Finding the ideal balance is critical for long-term machine reliability.
The Fit Categories
Clearance: Always a gap; allows movement.
Transition: May be a gap or an interference; used for location.
Interference: Always a “tight” overlap; requires force for assembly.
Interactive Tolerance & Fit Calculator
Enter your nominal dimension and select your desired hole and shaft designations to calculate the maximum and minimum limits. This tool ensures your specs align with ISO 286 (and its US adoption, ASME B4.2).
ISO Tolerance & Fit Calculator
Calculate precision limits and fit types for shafts and holes based on ISO 286 standards.
Identified Fit Type
H7/g6
Hole Limits
+21 / 0
Shaft Limits
-7 / -20
Max Clearance
0.041
Min Clearance
0.007
ISO 286 Precision Reference
0.00e+0 m
*Calculations based on ISO 286 standards. Values in microns (μm) and millimeters (mm).
H7/g6, H7/h6, and H8/f7 are common industrial clearance fits.
How to Use the ISO Fit Calculator
- Enter the nominal diameter in millimeters.
- Pick the hole tolerance class (for example H7).
- Pick the shaft tolerance class (for example g6).
- Read the upper and lower limits of each part, the maximum and minimum clearance or interference, and the fit type.
How the Limits Are Worked Out, with an Example
ISO 286-2 lists, for each size band, an upper and lower deviation for every tolerance class. Add them to the nominal size to get the limits. Clearance is the hole limit minus the shaft limit: maximum clearance = largest hole – smallest shaft, minimum clearance = smallest hole – largest shaft. A negative result is interference.
Example: 25 mm H7/g6. H7 for 18 to 30 mm is 0 to +21 µm, so the hole is 25.000 to 25.021 mm. g6 is -7 to -20 µm, so the shaft is 24.980 to 24.993 mm. Clearance runs from 0.007 mm to 0.041 mm: a precise sliding fit.
Press fit example: 25 mm H7/p6. p6 is +22 to +35 µm, so the shaft is 25.022 to 25.035 mm and the fit gives 0.001 to 0.035 mm of interference.
Key Tolerance Impacts
| Fit Strategy | Industrial Impact | Application Goal |
|---|---|---|
| Clearance Fits | Provides space for lubrication and thermal expansion. | Ensures smooth rotation. |
| Interference Fits | Uses friction and material elasticity to hold parts in place without fasteners. | Permanent, rigid joints. |
| Transition Fits | Allows for accurate centering while remaining easy to disassemble. | High-precision alignment. |
| IT Grades | Determines the "tightness" of the manufacturing window (IT01 to IT18). | Controls production costs. |
Frequently Asked Questions
What does H7/g6 mean?
H7 is the hole tolerance: the hole is never smaller than nominal and can be up to IT7 larger. g6 is the shaft tolerance: always slightly under nominal. Together they give a small, controlled clearance used for sliding and locating fits.
What is the tolerance for H7?
It depends on size. H7 is 0 to +21 µm for 18 to 30 mm, 0 to +25 µm for 30 to 50 mm and 0 to +12 µm for 3 to 6 mm, per ISO 286-2.
Which fit should I use for a bearing?
Bearing seats are chosen from the bearing maker’s tables because the bearing rings have their own tolerances. As a general guide, a rotating shaft carrying a rotating load often uses k5 or m5 and a housing H7, but check the bearing catalog for your load and speed.
What is the difference between a clearance, transition and interference fit?
A clearance fit always leaves a gap, a transition fit may give a small gap or a small interference, and an interference (press) fit always needs force or heating to assemble.
Next Steps
- Dowel and clevis pins: pins that rely on these fits
- Metric to inch converter: convert limits to inches
- Ask an engineer: help choosing a fit for a production part
- Request a quote for the fasteners in your joint.
Related Calculators
More free tools for the same job:
- Metric Thread Profile Calculator: Work out metric thread dimensions for correct fit.
- Tap Drill Size Calculator: Find the tap drill size before tapping a thread.
- Length Converter: Convert length between inches, millimeters, centimeters, meters and feet.
- Steel Weight Calculator: Estimate fastener weight by type, size and material.
Struggling with Complex Mating Parts?
Our engineering team can help you select the appropriate classes of fit to optimize your assembly process and reduce manufacturing rejects.