🔩 Clearance Hole Calculator
Calculate the correct hole size for bolts and screws
Diameter of the bolt or screw
Tolerance and clearance required
How to Use This Calculator
Enter Bolt Diameter
Input the diameter of the bolt or screw in inches. This is the nominal diameter (e.g., 0.5 for 1/2" bolt, 0.375 for 3/8" bolt).
Select Fit Type
Choose the fit type based on your application: Close Fit (minimum clearance), Normal Fit (standard clearance), or Loose Fit (generous clearance).
Calculate and Review
Click "Calculate Clearance Hole" to see clearance hole diameter, clearance amount, closest drill bit size, and clearance percentage. Use this for drilling holes.
Select Drill Bit
Use the closest drill bit size shown. If exact size isn't available, use the next larger standard drill bit size for easier assembly.
Formula
Clearance Hole Diameter = Bolt Diameter + Clearance
Close Fit: Clearance = +1/32" (0.031")
Normal Fit: Clearance = +1/16" (0.0625")
Loose Fit: Clearance = +1/8" (0.125")
Clearance % = (Clearance ÷ Bolt Diameter) × 100
Example 1: 1/2" Bolt (0.5"), Normal Fit
Step 1: Bolt diameter: 0.5 inches
Step 2: Normal fit clearance: +1/16" = +0.0625 inches
Step 3: Clearance hole diameter: 0.5 + 0.0625 = 0.5625 inches (9/16")
Step 4: Clearance: 0.5625 - 0.5 = 0.0625 inches (1/16")
Step 5: Closest drill bit: 9/16" (0.5625")
Example 2: 3/8" Bolt (0.375"), Close Fit
Step 1: Bolt diameter: 0.375 inches
Step 2: Close fit clearance: +1/32" = +0.031 inches
Step 3: Clearance hole diameter: 0.375 + 0.031 = 0.406 inches (13/32")
Step 4: Closest drill bit: 13/32" (0.406") or 7/16" (0.4375")
About Clearance Hole Calculator
The Clearance Hole Calculator is an essential tool for machinists, engineers, DIY enthusiasts, and contractors who need to determine the correct hole size for bolts and screws. This calculator eliminates guesswork by providing precise clearance hole calculations based on bolt diameter and fit type, helping you drill holes that are properly sized for bolt clearance.
When to Use This Calculator
- Drilling Holes: Calculate correct hole size for bolt and screw installations
- Machining: Determine clearance hole sizes for machining operations
- Assembly: Calculate hole sizes for assembly and fabrication projects
- Engineering: Determine clearance requirements for engineering applications
- Construction: Calculate hole sizes for construction and building projects
Why Use Our Calculator?
- ✅ Accurate Calculations: Precise calculations for proper bolt clearance
- ✅ Multiple Fit Types: Supports close fit, normal fit, and loose fit calculations
- ✅ Drill Bit Sizing: Shows closest standard drill bit size
- ✅ Metric Conversion: Converts to metric (mm) for international use
- ✅ Clearance Percentage: Shows clearance as percentage for easy comparison
- ✅ Time Savings: Instant calculations eliminate manual math and lookup tables
Common Applications
Drilling Holes: Machinists and DIY enthusiasts drilling holes for bolts use this calculator to determine correct hole size. Proper clearance prevents binding while maintaining alignment.
Machining: Engineers and machinists use this tool to calculate clearance hole sizes for machining operations, ensuring proper bolt fit and assembly.
Construction: Contractors and builders use this calculator to calculate hole sizes for construction projects, ensuring proper bolt clearance and installation.
Tips for Best Results
- Measure Accurately: Measure bolt diameter accurately (nominal diameter)
- Choose Fit Type: Use close fit for precision, normal fit for general use, loose fit for easy assembly
- Use Standard Drill Bits: Use closest standard drill bit size for easier drilling
- Consider Material: Harder materials may need slightly larger holes
- Consider Tolerance: Account for drill bit tolerance and hole accuracy
- Check Standards: For critical applications, consult engineering standards (ANSI, ISO)
Frequently Asked Questions
What size hole should I drill for a 1/2" bolt?
For a 1/2" bolt (0.5"), use normal fit for a 9/16" (0.5625") hole, or close fit for a 17/32" (0.531") hole, or loose fit for a 5/8" (0.625") hole. The calculator shows the exact size based on your fit type.
What's the difference between close fit, normal fit, and loose fit?
Close fit adds 1/32" clearance (minimum), normal fit adds 1/16" clearance (standard), and loose fit adds 1/8" clearance (generous). Choose based on your tolerance and assembly requirements.
Should I use exact hole size or next larger drill bit?
For easier assembly, use the next larger standard drill bit if the exact size isn't available. Slightly larger holes are easier to work with than holes that are too tight.
What if I don't have the exact drill bit size?
Use the next larger standard drill bit size. The calculator shows the closest standard drill bit size. Slightly larger holes are acceptable and make assembly easier.
Can I use this calculator for metric bolts?
Yes! Enter the bolt diameter in inches (convert from mm if needed). The calculator shows both imperial and metric results. For example, a 12mm bolt is approximately 0.472 inches.
What's the standard clearance for bolts?
Standard clearance is typically 1/16" (normal fit) for most applications. Close fit (1/32") is for precision applications, and loose fit (1/8") is for easy assembly or misalignment tolerance.