2026-07-30 8 min

Clearance Fit Calculator

Calculate clearance fit tolerance parameters per ISO 286 standard. Compute max/min clearance, allowance, and fit grade for hole-basis H7/g6 fits.

Calculator

Unit System

Nominal Diameter (mm)

Hole Tolerance

Shaft Tolerance

Results

Normal

Hole Tolerance

33.5202mm

Total tolerance zone for the hole (upper - lower deviation)

Shaft Tolerance

21.4529mm

Total tolerance zone for the shaft

Max Clearance

62.2052mm

Largest possible gap between hole and shaft

Min Clearance

7.2320mm

Smallest possible gap (allowance)

Allowance

7.2320mm

Minimum clearance (intentional gap) per ISO 286

Fit Type

Clearance

Classification of the fit based on tolerance zone overlap

Fit Grade

H7/g6

ISO 286 fit designation (e.g., H7/g6)

Visualizations

Results Overview

33.5mmHole Tolerance

21.5mmShaft Tolerance

62.2mmMax Clearance

7.2mmMin Clearance

7.2mmAllowance

76mmFit Grade

Formula

Clearance fit analysis per ISO 286-1:2010. Max clearance = hole upper deviation - shaft lower deviation. Min clearance = hole lower deviation - shaft upper deviation.

C_max = D_hole_upper - D_shaft_lower, C_min = D_hole_lower - D_shaft_upper

Alternative Form

Tol_hole = ES - EI, Tol_shaft = es - ei

Variables

Symbol	Name	Unit	Description
C_max	Max Clearance	mm	Maximum possible gap between hole and shaft
C_min	Min Clearance	mm	Minimum possible gap (allowance)
D_hole_upper	Hole Upper Deviation	mm	Upper deviation (ES) of hole tolerance zone
D_shaft_lower	Shaft Lower Deviation	mm	Lower deviation (ei) of shaft tolerance zone

Explanation

In a clearance fit, the hole tolerance zone lies entirely above the shaft tolerance zone, ensuring a positive gap between assembled parts. The hole-based system (H) uses a basic hole where lower deviation is zero. This is the most common ISO system for clearance fits.

Derivation

Tolerance values derive from ISO 286 standard tolerance grades. IT grades define the magnitude of the tolerance zone. Fundamental deviations (H for holes, a-z for shafts) define the position of the zone relative to the nominal size. The ISO tolerance unit i = 0.45 × ∛D + 0.001 × D defines the basic tolerance unit for grades 5-16.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Enter nominal diameter and select hole tolerance grade (H6, H7, H8).

Nominal Diameter:25 mm

Hole Grade:H7

Result: Hole: 0.0000/33.5202 mm

Step 2

Select shaft tolerance grade (g6, f7, e8, d9, c11, a11).

Shaft Grade:g6

Result: Shaft: -28.6850/-7.2320 mm

Step 3

Compute clearance values and verify fit type.

C_max = holeUpperDev - shaftLowerDev, C_min = holeLowerDev - shaftUpperDev

Max Clearance:62.2052 mm

Min Clearance:7.2320 mm

Intermediate: C_max = 33.5202 - -28.6850 = 62.2052

Result: Fit: Clearance (H7/g6)

Final Answer

33.5202

Worked Examples

See how the calculator works with different scenarios.

Scenario

A precision shaft with H7 hole and g6 shaft at 25 mm nominal diameter. Typical for sliding fits and precision positioning.

Inputs

Nominal Diameter:25 mm

Hole:H7

Shaft:g6

Calculation

i = 0.45×∛25 + 0.001×25 = 1.31 µm IT7 = 16×1.31 = 21 µm IT6 = 10×1.31 = 13 µm g6 upper = -2.5×25⁰·³³ ≈ -7 µm Max Clearance = 21 - (-20) = 41 µm Min Clearance = 0 - (-7) = 7 µm

Result

Clearance fit: 7-41 µm. Allowance = 7 µm

Interpretation

This provides excellent sliding clearance for precision shafts in bearings and guide mechanisms.

Understanding Your Result

Your Result: Hole Tolerance: 33.5202 mm

Typical range: H7/g6: 7-41 µm (precision sliding). H8/f7: 25-86 µm (normal running). H8/e8: 47-132 µm (loose running). H9/d9: 80-215 µm (free running). H11/c11: 0.15-0.45 mm (coarse clearance).

What This Means

A clearance fit ensures that the shaft will always be smaller than the hole when assembled. The minimum clearance (allowance) guarantees free relative motion between parts.

Why It Matters

Clearance fits are essential for rotating shafts, sliding mechanisms, and any assembly where parts must move relative to each other. Proper clearance prevents seizing, allows lubrication, and accommodates thermal expansion.

Professional Interpretation

ISO 286 clearance fits are categorized as: sliding fits (H7/g6), close running (H8/f7), normal running (H8/e8), loose running (H9/d9), and extra loose (H11/c11). The choice depends on speed, load, temperature, and lubrication requirements.

Recommendations

•Use H7/g6 for precision sliding fits with low-speed reciprocating motion
•Use H8/f7 for normal running fits with moderate speeds and oil lubrication
•Use H8/e8 for high-speed shafts requiring generous oil clearance
•Use H9/d9 for loose running fits with wide temperature variation
•Use H11/c11 or H11/a11 for coarse fits with no special requirements
•Always verify thermal expansion effects at operating temperature
•Consider surface finish effects on effective clearance

Educational Content

Introduction

A clearance fit is a type of fit in which the shaft is always smaller than the hole, guaranteeing a positive gap. This is the most common fit type for moving parts in mechanical assemblies.

Concept Explanation

In ISO 286, fits are defined by combining hole and shaft tolerance zones. The clearance fit occurs when the hole's lower deviation (minimum size) is greater than or equal to the shaft's upper deviation (maximum size). The hole-basis system (H) is preferred, where the hole's lower deviation is zero.

Applications

▸Sliding bearings and bushings

▸Piston-cylinder assemblies

▸Guide rails and linear motion systems

▸Rotating shaft supports

▸Hydraulic/pneumatic cylinder bores

▸Precision instrument spindles

▸Automotive engine valve guides

Benefits

•Ensures free relative motion between parts
•Allows oil film formation for lubrication
•Accommodates thermal expansion differences
•Simplifies assembly and disassembly
•Reduces risk of seizing under load
•Provides predictable running behavior

Limitations

•May introduce play or backlash in positioning systems
•Reduces accuracy of concentricity
•Can cause vibration at high speeds if too loose
•Wears over time increasing clearance

Best Practices

•Always use hole-basis system (H) for holes unless design conditions dictate otherwise
•Consider operating temperature range when selecting fit
•Account for surface roughness effect on effective clearance
•Verify minimum clearance allows adequate lubricant film thickness
•Use tighter clearances for oscillating motion, looser for continuous rotation
•Document fit requirements on drawings using ISO standard notation

Common Misconceptions

Myth: Tighter clearance always means better precision.

Truth: Too tight can cause seizing from thermal expansion or inadequate lubrication. Optimal clearance balances precision against functional reliability.

Myth: Clearance fits are only for moving parts.

Truth: Some stationary parts use clearance fits for ease of assembly, secured by set screws or adhesive.

Myth: Any H/g combination gives a clearance fit.

Truth: Some H/n or H/m combinations produce transition fits. Only H with shaft positions a-h give guaranteed clearance.

Practical Tips

•Always verify minimum clearance at maximum material condition (MMC)
•Consider plating or coating thickness that reduces effective clearance
•For high-temperature applications, use looser fits to account for thermal expansion
•Surface finish peaks can reduce effective clearance by 10-30% of Ra value
•Document both hole and shaft tolerances on assembly drawings
•Use go/no-go gages to verify actual clearance during production
•Consider statistical tolerance analysis for mass production
•For precision fits, specify roundness and cylindricity in addition to size

Common Mistakes

Confusing upper and lower deviations for holes vs shafts

Remember: For holes (H), ES = upper deviation (always positive), EI = lower deviation (0 for H). For shafts (a-h), es = upper deviation (negative for g, f, e, d), ei = lower deviation (more negative).

Using nominal size when calculating actual clearance

Clearance is calculated from deviations, not from nominal size. The nominal size is the starting reference point for both hole and shaft.

Ignoring form errors (roundness, cylindricity)

Add form tolerance requirements on the drawing. Actual clearance can be reduced by 50% or more if parts are out-of-round.

Not accounting for assembly temperature differences

Calculate thermal expansion effects if assembly temperature differs from operating temperature. Use coefficient of thermal expansion for materials.

Assumptions

This calculator makes the following assumptions to provide estimates:

Room Temperature Reference: All tolerance values are defined at 20°C (68°F) reference temperature per ISO 1.

Circular Cross-Section: Hole and shaft are assumed perfectly circular. Form errors require additional tolerance specifications.

Standard Material Elasticity: Deformation under assembly forces is not considered. For press fits and thin-walled parts, elastic deformation may affect clearance.

Clean, Dry Conditions: Surface contamination, lubricant film thickness, and corrosion buildup are not included.

Limitations

Be aware of these limitations when using this calculator:

Approximated Deviations: Fundamental deviations are approximated using power-law formulas. Exact ISO 286 table values may differ slightly for some diameter ranges.

Limited Grade Range: This calculator supports IT grades 4-11. Very fine (IT01-IT3) and very coarse (IT12-IT18) grades are not included.

No Temperature Compensation: Thermal expansion effects must be calculated separately for applications with significant temperature variation.

Single Fit Analysis: Each calculation considers one fit pair. For systems with multiple fits, analyze each interface separately.

Frequently Asked Questions

Answers to common questions about this calculator.

What is a clearance fit?

A clearance fit is a fit where the shaft is always smaller than the hole, ensuring a positive gap between parts when assembled. It allows free relative motion.

What does H7/g6 mean?

H7/g6 is an ISO 286 fit designation. H7 means the hole has a fundamental deviation of H (lower deviation = 0) with IT7 tolerance grade. g6 means the shaft has a g fundamental deviation with IT6 grade.

How is clearance fit calculated?

Max Clearance = Hole Upper Deviation - Shaft Lower Deviation. Min Clearance = Hole Lower Deviation - Shaft Upper Deviation. The fit is clearance if min clearance ≥ 0.

What is the difference between clearance and interference fit?

In a clearance fit, the shaft is always smaller than the hole (positive gap). In an interference fit, the shaft is always larger than the hole (negative gap, requiring force to assemble).

What is the hole-basis system?

The hole-basis system uses a basic hole (H) where the lower deviation is zero. The shaft tolerance is varied to achieve different fit types. This is the preferred ISO system.

What is an allowance in fits?

Allowance is the intentional minimum clearance (or maximum interference) designed into a fit. For clearance fits, allowance = min clearance.

What shaft grades give clearance fits with H holes?

Shaft positions a through h produce clearance fits when combined with H holes. The clearance decreases from a (largest) to h (smallest).

What is IT grade?

International Tolerance (IT) grade defines the magnitude of the tolerance zone. IT6 is finer than IT7. Standard grades range from IT01 (finest) to IT18 (coarsest).

How do I choose the right clearance fit?

Consider: function (sliding, running, free), speed, load, lubrication type, temperature range, material properties, and manufacturing capability. Use standard recommendations as starting point.

What is the typical clearance for H7/g6 at 25 mm?

For a 25 mm H7/g6 fit, the clearance range is approximately 7 µm (minimum) to 41 µm (maximum). This is a standard precision sliding fit.

What is the ISO 286 standard?

ISO 286 is the international standard for ISO code system for tolerances on linear sizes. It defines the system of fundamental deviations and IT grades for holes and shafts.

How does surface finish affect clearance?

Surface roughness peaks can reduce effective clearance. Typically, 10-30% of the Ra value reduces the functional clearance. For precision fits, specify surface finish requirements.

Can clearance fit be used for stationary parts?

Yes. Clearance fits are also used for stationary parts that need to be easily assembled/disassembled, with additional fasteners (set screws, keys) for torque transmission.

What is the difference between H7/g6 and H7/h6?

H7/g6 has a minimum clearance (g shaft has negative upper deviation). H7/h6 has zero minimum clearance (h shaft has zero upper deviation), which is a transition fit at MMC.

How does temperature affect clearance?

Thermal expansion changes the actual size of parts. If the shaft and hole have different temperatures or materials, clearance can increase or decrease significantly.

What are common clearance fit applications?

Sliding bearings, piston-cylinder, guide rails, linear bushings, gear shafts, motor mounts, and general rotating machinery.

How do I measure clearance?

Clearance can be measured using feeler gauges, dial indicators, coordinate measuring machines (CMM), or by subtracting measured shaft diameter from measured hole diameter.

What is maximum material condition (MMC)?

MMC is the condition where a feature contains the maximum amount of material (smallest hole, largest shaft). Clearance is minimized at MMC.

Can I mix hole-basis and shaft-basis in one design?

Technically yes, but it is poor practice. Always use one system consistently (preferably hole-basis) throughout a design to avoid confusion and reduce tooling costs.

What is IT5 vs IT6 vs IT7?

IT5, IT6, IT7 are tolerance grades with increasing tolerance values. IT5 ≈ 7.5i, IT6 ≈ 10i, IT7 ≈ 16i where i is the tolerance unit. IT7 is about 60% looser than IT6.

How do I specify clearance fit on a drawing?

Use ISO notation: e.g., ø25 H7/g6. The hole dimension shows ø25 H7, the shaft shows ø25 g6. On assembly drawings, show the fit as ø25 H7/g6.

What is the difference between running fit and sliding fit?

Sliding fits (H7/g6) have minimal clearance for precise slow motion. Running fits (H8/f7 or H8/e8) have more clearance for continuous rotation with lubrication.

How does wear affect clearance fits?

Wear increases clearance over time. Initial clearance should be selected considering expected wear life. Harder surface treatments can extend fit life.

What materials work best with clearance fits?

Most engineering materials can be used. Common pairs include steel shaft/bronze bushing, hardened steel/steel, and stainless steel/polymer bearings.

Can clearance fit cause vibration?

Yes, excessive clearance in rotating shafts can cause vibration, especially at high speeds. This is why precision balancing and proper fit selection are critical.

What is the cost impact of tight tolerances?

Tolerances tighter than IT6 significantly increase manufacturing cost. For general applications, IT7 for holes and IT6 for shafts provides good value.

How do plated coatings affect fits?

Plating adds material to the surface, reducing clearance. Account for plating thickness in the tolerance calculation, or specify tolerances for the final plated condition.

What is the shaft-basis system?

The shaft-basis system uses a basic shaft (h) where the upper deviation is zero. It is used when standard shafts (e.g., from stock) are available and holes must be custom.

How does lubrication film thickness relate to clearance?

Minimum clearance must be greater than the expected oil film thickness (typically 1-5 µm for hydrodynamic bearings). Too little clearance prevents oil film formation.

What is the difference between bilateral and unilateral tolerances?

Unilateral tolerance varies in one direction from nominal (e.g., H7). Bilateral tolerance varies in both directions (e.g., ±0.1). ISO 286 uses unilateral for holes and shafts.

How do I convert between clearance fit and tolerance classes?

Use ISO 286 tolerance tables or standards. The clearance calculation converts deviation values to actual clearance ranges for the given nominal size.

Related Calculators

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Related Guides

Deepen your understanding with these educational resources.

ISO 286 Tolerance System Guide

Engineering Toolbox guide to ISO limits and fits

Machine Design Fits and Tolerances Guide

Machine Design articles on fit selection

GD&T Tolerance Analysis Guide

EFunda ISO tolerance reference

Glossary

Technical terms used in mortgage calculations explained in plain language.

Allowance: The intentional minimum clearance or maximum interference in a designed fit.
Bilateral Tolerance: A tolerance that varies in both directions from the nominal dimension.
Clearance Fit: A fit where the shaft is always smaller than the hole, producing a positive gap.
ES/EI: Upper (ES) and Lower (EI) deviations for internal features (holes) per ISO 286.
es/ei: Upper (es) and Lower (ei) deviations for external features (shafts) per ISO 286.
Fit Grade: Designation combining hole and shaft tolerance classes, e.g., H7/g6.
Fundamental Deviation: The position of the tolerance zone relative to the nominal size (letter designation).
Hole-Basis System: Preferred ISO system where the hole has fixed H deviation and shaft tolerance is varied to achieve desired fit.
IT Grade: International Tolerance grade defining the magnitude of the tolerance zone width.
Maximum Clearance: The largest possible gap between the assembled hole and shaft.
Minimum Clearance: The smallest possible gap between the assembled hole and shaft, also called allowance.
Nominal Size: The basic reference dimension from which deviations are measured.
Shaft-Basis System: Alternative system where the shaft has fixed h deviation and hole tolerance is varied.
Tolerance Zone: The range between upper and lower deviations defining acceptable part dimensions.
Unilateral Tolerance: A tolerance that varies in only one direction from the nominal dimension.

Authoritative References

Trusted sources and standards referenced by this calculator.

ISO 286-1:2010 - ISO Code System for Tolerances on Linear Sizes ISO 286-2:2010 - Tables of Standard Tolerance Grades and Limit Deviations ISO 2768-1:1989 - General Tolerances for Linear and Angular Dimensions ASME Y14.5M - Dimensioning and Tolerancing ISO 8015:2011 - Geometrical Product Specifications (GPS) ISO 1101:2017 - Geometrical Tolerancing ISO 5459:2011 - Datums and Datum Systems

Applicable Standards

ISO 286-1ISO 286-2ISO 2768-1ASME Y14.5MISO 8015ISO 1101ISO 5459

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Last Updated:

2026-07-30

Version:

2.0.0

References:

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Free to use for educational and professional purposes.