Bearing Fit Calculator | Tolerance, Clearance and Interference Tool

Calculator Inputs

Nominal diameter (mm)

Hole grade

Shaft position

Shaft grade

Housing material preset

Housing thermal expansion coefficient (1/°C)

Housing temperature change (°C)

Shaft material preset

Shaft thermal expansion coefficient (1/°C)

Shaft temperature change (°C)

Assembly loss allowance (µm)

Safety margin (µm)

Measured housing bores (mm)

Measured shaft seats (mm)

Example Data Table

Case	Nominal Diameter	Hole Grade	Shaft Zone	Temperature Shift	Allowance Inputs	Typical Outcome
Easy-running assembly	50.000 mm	H7	g6	0 °C / 0 °C	2 µm loss, 2 µm margin	Close or running clearance fit
General location fit	50.000 mm	H7	js6	5 °C / 5 °C	2 µm loss, 3 µm margin	Transition fit
Press mounted bearing seat	50.000 mm	H7	k6	0 °C / 10 °C	2 µm loss, 3 µm margin	Light interference or transition
Heavy retention condition	50.000 mm	H7	m6	-5 °C / 15 °C	3 µm loss, 5 µm margin	Medium interference fit

Formula Used

This calculator uses ISO-style tolerance concepts for quick fit estimation. It combines tolerance grades, shaft position estimates, thermal growth, and optional process capability checks.

Tolerance unit: i = 0.45 × ∛D + 0.001D in microns, where D is nominal diameter in millimeters.
IT tolerance: IT = factor × i. Common factors are 7, 10, 16, 25, 40, 64, and 100 for grades 5 to 11.
Hole limits: Hole min = D + EI/1000 and Hole max = D + ES/1000.
Shaft limits: Shaft min = D + ei/1000 and Shaft max = D + es/1000.
Basic fit range: Min clearance = Hole min − Shaft max, Max clearance = Hole max − Shaft min.
Thermal growth: Δsize = α × D × ΔT.
Adjusted operating clearance: Operating clearance − assembly loss − safety margin.
Process capability: Cpk = min[(USL − mean)/(3s), (mean − LSL)/(3s)].

Positive clearance means looseness. Negative clearance means interference. For production release, always compare with the exact fit table required by your drawing or applicable standard.

How to Use This Calculator

Enter the nominal diameter of the bearing seat in millimeters.
Select the hole grade, usually a hole-basis choice such as H7.
Choose the shaft position and grade that match your intended fit.
Set housing and shaft material presets or type custom thermal coefficients.
Enter temperature changes if service temperature differs from inspection temperature.
Add assembly loss and safety margin to reflect roughness, settling, or risk tolerance.
Optionally paste measured bore and shaft values to evaluate process capability.
Press the calculate button to view the result above the form, inspect the tables, and review the Plotly fit-zone graph.

FAQs

1. What does this bearing fit calculator do?

It estimates hole and shaft limit sizes, basic clearance or interference, temperature-adjusted fit, assembly-adjusted fit, and optional Cpk values for housing bores and shaft seats.

2. What does a negative clearance value mean?

A negative clearance means the shaft is larger than the hole at that condition. That creates interference and usually requires press, thermal, or shrink assembly methods.

3. Why does temperature matter in bearing fits?

Shafts and housings expand at different rates. A fit that looks acceptable at room temperature can become loose or excessively tight during service.

4. Why are sample measurements optional?

Design limits define the intended fit, but measured values show what production is actually delivering. Sample data helps estimate process centering, spread, and capability.

5. What is Cpk in this calculator?

Cpk compares the sample mean and variation against the specification limits. Higher Cpk usually means the machining process is more capable and more stable.

6. Should I always use H7 for the bore?

Not always. H7 is common for hole-basis work, but actual bearing seats depend on load, rotation, material, speed, mounting practice, and the standard specified on the drawing.

7. Why include assembly loss and safety margin?

They let you reduce theoretical clearance to account for settling, roughness, coatings, measurement uncertainty, or a tighter quality-control decision rule.

8. Are these results enough for final production approval?

Use them for engineering screening and quality review. Final release should still confirm official fit tables, bearing manufacturer guidance, and your controlled drawing requirements.