🔩 Thread Calculator
Calculate thread dimensions and properties
Nominal thread diameter
1 / threads per inch (TPI)
How to Use This Calculator
Select Thread Type
Choose thread type (Unified, Metric, ACME, or Buttress). Most common are Unified (UNC/UNF) and Metric threads.
Enter Major Diameter
Input major diameter (nominal thread diameter) in inches. For example, 1/2" = 0.500", 3/8" = 0.375".
Enter Thread Pitch
Input thread pitch in inches (1 / threads per inch). For example, 13 TPI = 1/13 = 0.0769", 20 TPI = 1/20 = 0.050".
Calculate and Review
Click "Calculate Thread Dimensions" to see pitch diameter, minor diameter, thread height, threads per inch, lead angle, and stress area.
Formula
Pitch Diameter: PD = D - 0.6495 × P
Minor Diameter: MD = D - 1.299 × P
Thread Height: H = 0.866 × P
where: D = major diameter, P = thread pitch
Example 1: 1/2-13 UNC (D = 0.500", P = 1/13 = 0.0769")
Step 1: Pitch Diameter = D - 0.6495 × P = 0.500 - 0.6495 × 0.0769 = 0.450"
Step 2: Minor Diameter = D - 1.299 × P = 0.500 - 1.299 × 0.0769 = 0.400"
Step 3: Thread Height = 0.866 × P = 0.866 × 0.0769 = 0.067"
Step 4: Threads per Inch = 1 / P = 1 / 0.0769 = 13 TPI
Example 2: M12×1.75 (D = 12 mm = 0.472", P = 1.75 mm = 0.069")
Step 1: Pitch Diameter = 0.472 - 0.6495 × 0.069 = 0.427"
Step 2: Minor Diameter = 0.472 - 1.299 × 0.069 = 0.382"
About Thread Calculator
The Thread Calculator is an essential tool for machinists, mechanical engineers, and thread designers who need to calculate thread dimensions and properties for threaded fasteners. This calculator implements standard thread formulas for unified, metric, ACME, and buttress threads, helping you determine thread specifications and ensure proper thread engagement.
When to Use This Calculator
- Thread Design: Calculate thread dimensions for thread design and manufacturing
- Thread Measurement: Determine thread dimensions for thread inspection
- Fastener Selection: Verify thread dimensions for fastener selection
- Thread Analysis: Analyze thread dimensions and tolerances
- Educational Use: Learn and understand thread calculations
Why Use Our Calculator?
- ✅ Multiple Thread Types: Supports Unified, Metric, ACME, and Buttress threads
- ✅ Accurate Formulas: Uses standard thread equations
- ✅ Complete Dimensions: Shows pitch diameter, minor diameter, thread height, and TPI
- ✅ Thread Properties: Calculates lead angle, engagement length, and stress area
- ✅ Time Savings: Instant calculations eliminate manual math
Understanding Thread Dimensions
Basic Principle: Thread dimensions include major diameter (outer diameter), pitch diameter (diameter at thread pitch line), minor diameter (root diameter), and thread height (height of thread triangle). Pitch diameter is critical for thread engagement and fit. Thread height determines thread strength.
Thread Pitch: Thread pitch is the distance between adjacent thread crests. For unified threads, pitch = 1 / TPI (threads per inch). For metric threads, pitch is specified directly in millimeters (e.g., M12×1.75 has pitch = 1.75 mm).
Thread Classes: Thread classes (1A, 2A, 3A for external, 1B, 2B, 3B for internal) specify tolerances. Class 1 = loose fit (large tolerances), Class 2 = standard fit (medium tolerances), Class 3 = close fit (tight tolerances). The calculator shows thread class for reference.
Tips for Best Results
- Accurate Measurements: Use actual major diameter and pitch from thread specifications
- Correct Thread Type: Select appropriate thread type for accurate calculations
- Verify with Standards: Check thread standards (ANSI, ISO) for exact values
- Consider Tolerances: Account for thread class tolerances in design
- Check Thread Engagement: Ensure proper thread engagement based on pitch diameter
Frequently Asked Questions
How do I calculate thread dimensions?
Pitch Diameter = Major Diameter - (0.6495 × Thread Pitch). Minor Diameter = Major Diameter - (1.299 × Thread Pitch). Thread Height = 0.866 × Thread Pitch. For example, 1/2-13 UNC (D = 0.500", P = 0.0769"): PD = 0.450", MD = 0.400", H = 0.067". The calculator does this automatically.
What is the difference between major and pitch diameter?
Major diameter is the outer diameter of the thread (nominal thread size), while pitch diameter is the diameter at the thread pitch line (typically 0.6495 × pitch smaller than major diameter). Pitch diameter is critical for thread engagement and fit. Minor diameter is the inner diameter (root diameter), typically 1.299 × pitch smaller than major diameter.
How do I convert threads per inch to pitch?
Thread pitch (in inches) = 1 / Threads Per Inch (TPI). For example, 13 TPI = 1/13 = 0.0769", 20 TPI = 1/20 = 0.050". For metric threads, pitch is specified directly in millimeters (e.g., M12×1.75 has pitch = 1.75 mm = 0.069").
What are standard thread sizes?
Standard unified thread sizes: #4, #6, #8, #10, #12, 1/4", 5/16", 3/8", 7/16", 1/2", 9/16", 5/8", 3/4", 7/8", 1", etc. Standard metric sizes: M3, M4, M5, M6, M8, M10, M12, M16, M20, etc. Thread pitch varies by size and thread series (UNC, UNF, UNEF).
Does thread class affect dimensions?
Thread class affects tolerances, not calculated dimensions. Pitch diameter calculation is the same for all thread classes, but tolerance limits vary. Class 1 = loose fit (large tolerances), Class 2 = standard fit (medium tolerances), Class 3 = close fit (tight tolerances). The calculator shows thread class for reference but uses standard pitch diameter formula.