Tolerance Calculator
Calculate geometric tolerances, fits, and clearances based on ISO and ANSI standards for precision manufacturing. Supports GD&T, dimensional tolerances, and surface finish specifications with professional engineering accuracy.
Dimensional Tolerance Calculator
Dimension Specification
Tolerance Analysis
Geometric Tolerance (GD&T) Calculator
GD&T Specification
GD&T Analysis
Fits & Clearances Calculator
Fit Specification
Fit Analysis
Surface Finish Calculator
Surface Specification
Surface Analysis
Tolerance Reference Tables
| IT Grade | Tolerance (μm) | Application | Machining Process |
|---|
| Fit Class | Type | Application | Assembly Method |
|---|
| Ra (μm) | Ra (μin) | Application | Process |
|---|
| Symbol | Characteristic | Type | Datum Required |
|---|
Understanding Tolerance Systems and Manufacturing Standards
Dimensional Tolerances
IT Tolerance System: International Tolerance grades from IT01 (±0.0005mm) to IT18 (±2.5mm) define precision levels.
Fundamental Deviations: Upper case letters (A-ZC) for holes, lower case (a-zc) for shafts determine fit types.
Size Range Factors: Tolerance values scale with nominal size: 0-3mm, 3-6mm, 6-10mm ranges have different coefficients.
Process Capability: Turning (IT7-IT9), Milling (IT8-IT10), Grinding (IT5-IT7) typical achievable grades.
Geometric Tolerances (GD&T)
Form Controls: Straightness, Flatness, Circularity, Cylindricity control individual feature shape without datums.
Orientation Controls: Perpendicularity, Parallelism, Angularity require datum references for orientation control.
Location Controls: Position tolerance defines true position within diameter zone, critical for assembly.
Material Conditions: MMC provides bonus tolerance, LMC ensures minimum material, RFS applies at all sizes.
Fits and Clearances
Clearance Fits: Always provide clearance (H7/g6, H8/f7) for running fits and easy assembly.
Transition Fits: May have clearance or interference (H7/k6, H7/n6) for precise location.
Interference Fits: Always interference (H7/p6, H7/s6) for permanent assembly without fasteners.
Assembly Methods: Hand (0-25μm clearance), Press (25-75μm interference), Shrink (>100μm interference).
Surface Finish
Ra (Arithmetic Average): Most common parameter, average of absolute deviations from mean line.
Rz (Ten Point Height): Average of five highest peaks and lowest valleys, better for functional surfaces.
Process Capabilities: Rough machining (Ra 25μm), Finish machining (Ra 3.2μm), Grinding (Ra 0.8μm), Polishing (Ra 0.1μm).
Functional Relationship: Bearing surfaces require Ra 0.1-0.8μm, Sealing surfaces Ra 0.4-1.6μm.
Frequently Asked Questions
The tolerance calculator supports both ISO (International Organization for Standardization) and ANSI (American National Standards Institute) tolerance standards.
Supported standards include:
- IT tolerance grades: IT01 (±0.0005mm precision) to IT18 (±2.5mm general)
- Geometric tolerances (GD&T): Form, orientation, location, and runout controls
- Standard fit classes: H7/g6, H8/f7, H7/k6, H7/p6, and custom fits
- Surface finish specifications: Ra, Rz, Rmax parameters in metric and imperial units
- Material conditions: MMC, LMC, and RFS for comprehensive tolerance analysis
All calculations comply with international engineering standards for global manufacturing compatibility.
Follow these steps to calculate GD&T tolerances:
- Select Geometric Tolerance tab and choose the appropriate characteristic:
- Form tolerances: Straightness (⎯), Flatness (⏸), Circularity (○), Cylindricity (⌭)
- Orientation tolerances: Perpendicularity (⊥), Parallelism (∥), Angularity (∠)
- Location tolerances: Position (⊕), Concentricity (◎), Symmetry (≡)
- Runout tolerances: Circular runout (↗), Total runout (↗↗)
- Specify tolerance value based on functional requirements
- Select material condition: MMC (maximum material), LMC (least material), or RFS (regardless of feature size)
- Enter feature size and tolerance for bonus tolerance calculations
The calculator generates the proper GD&T symbol frame and analyzes tolerance zones for CNC programming and inspection.
The three main types of fits serve different assembly and functional requirements:
Clearance Fits
- H7/g6, H8/f7, H9/d9: Always provide clearance between mating parts
- Applications: Bearings, sliding fits, easy assembly/disassembly
- Assembly: Hand assembly, no force required
Transition Fits
- H7/k6, H7/n6: May have either clearance or interference depending on manufacturing variations
- Applications: Precise location, alignment pins, locating features
- Assembly: Light press or hand assembly depending on actual sizes
Interference Fits
- H7/p6 (light), H7/s6 (medium), H7/u6 (heavy): Always create interference
- Applications: Permanent assembly, gear hubs, press fits
- Assembly: Press, shrink, or hydraulic fitting required
IT tolerance grades should match your machining process capabilities:
Standard CNC Operations
- Turning: IT7-IT9 (±0.012-0.030mm) - Good for general shaft work
- Milling: IT8-IT10 (±0.018-0.048mm) - Standard for most CNC milling
- Drilling: IT9-IT11 (±0.030-0.075mm) - Typical for hole location
- Boring: IT6-IT8 (±0.008-0.018mm) - Precision hole sizing
- Reaming: IT6-IT7 (±0.008-0.012mm) - Final hole finishing
Precision Operations
- Grinding: IT5-IT7 (±0.006-0.012mm) - High precision finishing
- Honing: IT4-IT6 (±0.004-0.008mm) - Cylinder bore finishing
- Lapping: IT3-IT5 (±0.003-0.006mm) - Ultra-precision surfaces
Recommendation: For general CNC work, IT7-IT8 provides excellent balance between precision and manufacturability. Specify tighter tolerances (IT5-IT6) only when functionally required.
Surface finish directly impacts both achievable tolerances and functional performance:
Tolerance-Surface Finish Relationships
- IT5-IT6 tolerances: Require Ra 0.4-0.8μm (grinding/polishing operations)
- IT7-IT8 tolerances: Work with Ra 1.6-3.2μm (finish machining operations)
- IT9-IT10 tolerances: Accept Ra 6.3-12.5μm (rough machining operations)
- IT11+ tolerances: Compatible with Ra 12.5-25μm (rough operations)
Functional Surface Requirements
- Bearing surfaces: Ra 0.1-0.8μm for proper lubrication and wear resistance
- Sealing surfaces: Ra 0.4-1.6μm for O-ring grooves and gasket surfaces
- Sliding contacts: Ra 0.8-3.2μm for smooth operation and reduced friction
- General surfaces: Ra 3.2-6.3μm for non-critical cosmetic appearance
Key Rule: Surface finish should be approximately 1/10 of the tolerance value for optimal precision. Specifying unnecessarily fine surface finishes increases manufacturing cost without functional benefit.