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📊 Aviation Conversion Quick Reference
Common conversions mechanics use every day — organized into at-a-glance cards. Fractions, decimals, torque, pressure, temperature, and more.
📏 Fractions to Decimals (Inches)
1/64 — 1/2 Inch
| Fraction | Decimal | mm |
|---|---|---|
| 1/64" | 0.0156" | 0.397 |
| 1/32" | 0.0313" | 0.794 |
| 3/64" | 0.0469" | 1.191 |
| 1/16" | 0.0625" | 1.588 |
| 5/64" | 0.0781" | 1.984 |
| 3/32" | 0.0938" | 2.381 |
| 7/64" | 0.1094" | 2.778 |
| 1/8" | 0.1250" | 3.175 |
| 9/64" | 0.1406" | 3.572 |
| 5/32" | 0.1563" | 3.969 |
| 11/64" | 0.1719" | 4.366 |
| 3/16" | 0.1875" | 4.763 |
| 13/64" | 0.2031" | 5.159 |
| 7/32" | 0.2188" | 5.556 |
| 15/64" | 0.2344" | 5.953 |
| 1/4" | 0.2500" | 6.350 |
17/64 — 1 Inch
| Fraction | Decimal | mm |
|---|---|---|
| 17/64" | 0.2656" | 6.747 |
| 9/32" | 0.2813" | 7.144 |
| 19/64" | 0.2969" | 7.541 |
| 5/16" | 0.3125" | 7.938 |
| 21/64" | 0.3281" | 8.334 |
| 11/32" | 0.3438" | 8.731 |
| 23/64" | 0.3594" | 9.128 |
| 3/8" | 0.3750" | 9.525 |
| 25/64" | 0.3906" | 9.922 |
| 13/32" | 0.4063" | 10.319 |
| 7/16" | 0.4375" | 11.113 |
| 15/32" | 0.4688" | 11.906 |
| 1/2" | 0.5000" | 12.700 |
| 9/16" | 0.5625" | 14.288 |
| 5/8" | 0.6250" | 15.875 |
| 1" | 1.0000" | 25.400 |
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🧮 Key Conversion Formulas
Temperature
°C = (°F − 32) × 5/9
°F = (°C × 9/5) + 32
ISA standard day: 59°F (15°C) at sea level
Torque
N·m = ft·lb × 1.35582
ft·lb = in·lb ÷ 12
Always verify torque spec from AMM
Pressure
bar = PSI × 0.0689476
kPa = PSI × 6.89476
1 atm = 14.696 PSI = 1.01325 bar = 101.325 kPa
Length
mm = inches × 25.4
meters = feet × 0.3048
1" = 25.4 mm exactly
Weight
kg = lb × 0.453592
lb = kg × 2.20462
Fuel: Jet-A ≈ 6.7 lb/US gal (varies with temperature)
Volume / Fuel
liters = US gal × 3.78541
US gal = liters × 0.26417
Avgas ≈ 6.0 lb/US gal | Jet-A ≈ 6.7 lb/US gal
Torque Wrench Extension
TW = (TS × L) ÷ (L + E)
TW = wrench reading | TS = target torque | L = wrench effective length | E = extension length. Measure both from the drive centerline.
Rivet Hole Diameter
Hole = rivet dia. + 0.002" to 0.004"
Per AC 43.13. Minimum edge distance = 2× rivet diameter. Minimum pitch = 3× rivet diameter.
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📌 Numbers Every Aviation Mechanic Should Know
ISA Standard Atmosphere
| Parameter | Sea Level Value |
|---|---|
| Temperature | 59°F / 15°C |
| Pressure | 14.696 PSI / 29.92" Hg / 1013.25 hPa |
| Density | 0.002377 slug/ft³ |
| Speed of Sound | 661.5 ktas / 340.3 m/s |
| Lapse Rate | −2°C per 1000 ft to 36,089 ft |
| Tropopause | 36,089 ft / −56.5°C |
Fuel Specific Gravity / Weight
| Fuel Type | lb/US gal | lb/liter |
|---|---|---|
| Jet-A / Jet-A1 | ~6.7 | ~0.802 |
| JP-8 | ~6.7 | ~0.800 |
| Avgas 100LL | ~6.0 | ~0.715 |
| Avgas 100 | ~6.0 | ~0.720 |
| Skydrol 500B | ~8.8 | ~1.054 |
| Water | 8.34 | 1.000 |
Common Cotter Pin (MS24665) Sizes
| Bolt Size | Cotter Pin |
|---|---|
| AN3 / 10-32 | MS24665-132 (1/32") |
| AN4 / 1/4-28 | MS24665-132 or -140 (3/64") |
| AN5 / 5/16-24 | MS24665-140 (3/64") |
| AN6 / 3/8-24 | MS24665-151 (1/16") |
| AN7 / 7/16-20 | MS24665-151 (1/16") |
| AN8 / 1/2-20 | MS24665-162 (3/32") |
Metric vs. SAE Wrench Equivalents
| SAE (in) | Metric (mm) | Close? |
|---|---|---|
| 1/4" | 6 mm | 0.236" ≈ 1/4" |
| 5/16" | 8 mm | 0.315" ≈ 5/16" |
| 3/8" | 10 mm | 0.394" ≈ 3/8" |
| 7/16" | 11 mm | 0.433" close |
| 1/2" | 13 mm | 0.512" ≈ 1/2" |
| 9/16" | 14 mm | 0.551" close |
| 5/8" | 16 mm | 0.630" ≈ 5/8" |
| 3/4" | 19 mm | 0.748" ≈ 3/4" |