Home > Fasteners 101 > Unit Conversion Calculator
🔄 Unit Conversion Calculator
Convert between measurement systems instantly
Type a value in either box — the other updates automatically
in
⇄
mm
1 inch = 25.4 mm • 1 mm = 0.03937 inches
Common Fastener Sizes
| Inches | mm | Inches | mm |
|---|---|---|---|
| 1/4" (0.250) | 6.35 | 1/2" (0.500) | 12.70 |
| 5/16" (0.3125) | 7.94 | 5/8" (0.625) | 15.88 |
| 3/8" (0.375) | 9.53 | 3/4" (0.750) | 19.05 |
| 7/16" (0.4375) | 11.11 | 1" (1.000) | 25.40 |
Type a value in either box — the other updates automatically
ft-lbs
⇄
Nm
1 ft-lb = 1.356 Nm • 1 Nm = 0.738 ft-lb
Common Torque Values
| Application | ft-lbs | Nm |
|---|---|---|
| Spark plugs (typical) | 15-20 | 20-27 |
| Wheel lug nuts (car) | 80-100 | 108-136 |
| 1/4" Grade 5 bolt | 8 | 11 |
| 3/8" Grade 5 bolt | 31 | 42 |
| 1/2" Grade 5 bolt | 75 | 102 |
| 1/2" Grade 8 bolt | 105 | 142 |
Enter a decimal to find the nearest fractional inch
Nearest Fraction
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Decimal to Fraction Reference
| Fraction | Decimal | Fraction | Decimal | Fraction | Decimal |
|---|---|---|---|---|---|
| 1/16" | 0.0625 | 3/8" | 0.3750 | 11/16" | 0.6875 |
| 1/8" | 0.1250 | 7/16" | 0.4375 | 3/4" | 0.7500 |
| 3/16" | 0.1875 | 1/2" | 0.5000 | 13/16" | 0.8125 |
| 1/4" | 0.2500 | 9/16" | 0.5625 | 7/8" | 0.8750 |
| 5/16" | 0.3125 | 5/8" | 0.6250 | 1" | 1.0000 |
Find equivalent grades between SAE (inch) and Metric bolt systems
| SAE Grade | Metric Class | Tensile Strength | Typical Use |
|---|---|---|---|
| Grade 2 | 4.6 / 4.8 | 60,000 psi (414 MPa) | Non-critical, low stress |
| Grade 5 | 8.8 | 120,000 psi (827 MPa) | Automotive, general industrial |
| Grade 8 | 10.9 | 150,000 psi (1034 MPa) | High-stress, heavy equipment |
| — | 12.9 | 180,000 psi (1241 MPa) | Socket head cap screws |
| A325 | 8.8 | 120,000 psi min | Structural steel connections |
| A490 | 10.9 | 150,000 psi min | Heavy structural connections |
💡 How to Identify Bolt Grades
SAE Grades: Count the radial lines on the bolt head. Grade 5 = 3 lines, Grade 8 = 6 lines, Grade 2 = no lines.
Metric Classes: Look for numbers stamped directly on the head (8.8, 10.9, 12.9). The first number × 100 = tensile strength in MPa.
Stainless Steel Grades
| Grade | Marking | Tensile Strength | Notes |
|---|---|---|---|
| 18-8 / 304 | A2-70 | ~70,000 psi | General purpose stainless |
| 316 | A4-70 | ~70,000 psi | Marine grade (more corrosion resistant) |
| 18-8 / 304 | A2-80 | ~80,000 psi | Strain-hardened, higher strength |