Calculator Input
Formula Used
Hole minimum limit = nominal size + hole lower deviation.
Hole maximum limit = nominal size + hole upper deviation.
Shaft minimum limit = nominal size + shaft lower deviation.
Shaft maximum limit = nominal size + shaft upper deviation.
Minimum clearance = hole minimum limit - shaft maximum limit.
Maximum clearance = hole maximum limit - shaft minimum limit.
Fit range = maximum clearance - minimum clearance.
Adjusted clearance = calculated clearance - assembly allowance.
How to Use This Calculator
- Enter the nominal basic size from the drawing.
- Select the unit used for the basic size.
- Enter hole lower and upper deviations with correct signs.
- Enter shaft lower and upper deviations with correct signs.
- Select the deviation unit used on the drawing.
- Add assembly allowance when coating, heat, or reserve matters.
- Enter quantity and expected scrap rate for planning.
- Press calculate and review the result below the header.
- Use CSV or PDF export for records.
Example Data Table
| Nominal Size | Hole Lower | Hole Upper | Shaft Lower | Shaft Upper | Likely Result |
|---|---|---|---|---|---|
| 50 mm | 0 µm | 25 µm | -25 µm | -9 µm | Clearance fit |
| 50 mm | 0 µm | 25 µm | -5 µm | 18 µm | Transition fit |
| 50 mm | 0 µm | 25 µm | 35 µm | 55 µm | Interference fit |
Limits and Fits Calculator Guide
Purpose
A limits and fits calculator helps machinists compare the permitted size range of a hole with the permitted size range of a matching shaft. It turns drawing tolerances into clear shop values. You can see the lower limit, upper limit, tolerance width, minimum clearance, maximum clearance, and possible interference. These values guide inspection, setup, and assembly choices before parts reach the bench.
Calculation Method
The method starts with a basic size. Each deviation is added to that size. Hole lower deviation gives the smallest hole. Hole upper deviation gives the largest hole. Shaft lower deviation gives the smallest shaft. Shaft upper deviation gives the largest shaft. The calculator then subtracts shaft limits from hole limits. A positive minimum clearance means every assembly will be loose. A negative maximum clearance means every assembly will press together. Mixed signs show a transition fit.
Practical Use
This tool is useful when drawings use micrometers, millimeters, or inches. It also includes an assembly allowance field. Use that field for plating, coating, heat growth, dirt, or measurement reserve. The adjusted clearance values show the practical result after that allowance is removed. Quantity and scrap rate fields help estimate how many assemblies may need replacement parts or extra inspection.
Accuracy Notes
For accurate results, enter deviations with signs. A lower shaft deviation below the basic size should be negative. A hole marked H often has a zero lower deviation. Check the drawing standard before using preset values. Standards change by nominal size range and tolerance grade, so exact tables should be used for final production.
Decision Support
The result table is designed for quick decisions. Use a clearance fit for rotating, sliding, or removable parts. Use a transition fit for accurate location with possible light force. Use an interference fit for permanent joints, pulleys, bushings, and pressed collars. Always verify material strength, surface finish, and thermal conditions. Tolerances describe geometry. They do not replace engineering judgment. Good measurement habits are also important. Use calibrated tools. Measure at stable temperature. Clean parts before checking. Record both hole and shaft readings. Compare every reading with the limits shown here. Keep exported files with job travelers. They make repeat setups easier, especially when operators change shifts or suppliers send measured samples for approval later during audits too.
FAQs
What is a limit in machining?
A limit is the smallest or largest allowed part size. The part is acceptable when the measured size stays between those two values.
What is a fit?
A fit describes how a shaft and hole assemble. It may be loose, tight, or mixed depending on their tolerance zones.
What is minimum clearance?
Minimum clearance is the smallest possible space between the hole and shaft. It uses the smallest hole and largest shaft.
What is maximum clearance?
Maximum clearance is the largest possible space between the hole and shaft. It uses the largest hole and smallest shaft.
When is a fit called interference?
A fit is interference when the shaft is always larger than the hole. Assembly usually needs force, heat, or controlled pressing.
When is a fit called transition?
A transition fit happens when tolerance ranges overlap. Some parts may assemble with clearance, while others may need slight force.
Why are deviations entered with signs?
Signs show whether a limit is above or below the nominal size. Negative values reduce the size. Positive values increase it.
Can I use this for final production approval?
Use it for planning and checking calculations. Final approval should follow the drawing, inspection plan, material rules, and applicable tolerance standard.