Fractional Inches Converter
Convert fractional inches to decimal inches and millimeters with high precision. Perfect for woodworking, machining, and engineering applications.
Fractional Inches Converter
Common Fractions Quick Reference
1/64
0.016"
0.4mm
1/32
0.031"
0.8mm
3/64
0.047"
1.2mm
1/16
0.063"
1.6mm
5/64
0.078"
2.0mm
3/32
0.094"
2.4mm
7/64
0.109"
2.8mm
1/8
0.125"
3.2mm
9/64
0.141"
3.6mm
5/32
0.156"
4.0mm
11/64
0.172"
4.4mm
3/16
0.188"
4.8mm
13/64
0.203"
5.2mm
7/32
0.219"
5.6mm
15/64
0.234"
6.0mm
1/4
0.250"
6.3mm
17/64
0.266"
6.7mm
9/32
0.281"
7.1mm
19/64
0.297"
7.5mm
5/16
0.313"
7.9mm
21/64
0.328"
8.3mm
11/32
0.344"
8.7mm
23/64
0.359"
9.1mm
3/8
0.375"
9.5mm
Complete Fractional Inches Conversion Guide
Comprehensive guide to fractional inch measurements, decimal equivalents, and millimeter conversions
Understanding Fractional Inch Measurements
Fractional Inch System
- •Based on halving: 1/2, 1/4, 1/8, 1/16, 1/32, 1/64
- •Denominator doubles with each subdivision level
- •1/64 inch ≈ 0.397 mm (finest common fraction)
- •Used in US/UK construction, woodworking, plumbing
- •Tape measures typically marked to 1/16 inch
- •Precision instruments to 1/64 inch
Decimal & Metric Equivalents
- •1 inch = 25.4 mm exactly (by international agreement, 1959)
- •1 inch = 2.54 cm
- •1/2 inch = 12.7 mm
- •1/4 inch = 6.35 mm
- •1/8 inch = 3.175 mm
- •1/16 inch = 1.5875 mm
- •1/32 inch = 0.79375 mm
- •1/64 inch = 0.396875 mm
Fractional Inch Reference Table
Halves, Quarters & Eighths
- •1/2" = 0.500" = 12.700 mm
- •1/4" = 0.250" = 6.350 mm
- •3/4" = 0.750" = 19.050 mm
- •1/8" = 0.125" = 3.175 mm
- •3/8" = 0.375" = 9.525 mm
- •5/8" = 0.625" = 15.875 mm
- •7/8" = 0.875" = 22.225 mm
Sixteenths (1/16–15/16)
- •1/16" = 0.0625" = 1.588 mm
- •3/16" = 0.1875" = 4.763 mm
- •5/16" = 0.3125" = 7.938 mm
- •7/16" = 0.4375" = 11.113 mm
- •9/16" = 0.5625" = 14.288 mm
- •11/16" = 0.6875" = 17.463 mm
- •13/16" = 0.8125" = 20.638 mm
- •15/16" = 0.9375" = 23.813 mm
Thirty-Seconds & Sixty-Fourths
- •1/32" = 0.03125" = 0.794 mm
- •1/64" = 0.015625" = 0.397 mm
- •Common drill bit sizes: 1/16, 5/64, 3/32, 7/64, 1/8, 9/64, 5/32, 11/64, 3/16, 13/64, 7/32, 15/64, 1/4
- •Pipe thread nominal vs actual: 1/2" NPT OD = 0.840"
Professional Applications
Construction & Carpentry
- •Lumber nominal vs actual: 2×4 = 1.5"×3.5"
- •Drywall: 1/2" or 5/8" thick
- •Stud spacing: 16" O.C. (on center)
- •Ceiling height: 8', 9', 10'
- •Door width: 32", 34", 36"
- •Window rough opening: add 1/2" to each side
- •Plywood: 3/4", 1/2", 3/8", 1/4" sheets
Plumbing & HVAC
- •Pipe sizes nominal (not actual): 1/2" copper OD = 5/8"
- •3/4" copper OD = 7/8"
- •1/2" schedule 40 PVC OD = 0.840"
- •Duct dimensions in even inches
- •HVAC filter sizes: 16×20×1", 20×25×1"
- •Refrigerant tubing: 1/4", 3/8", 1/2", 5/8" OD
Machining & Manufacturing
- •Drill bit series: wire gauge, letter, fractional, metric
- •Fractional drill bits 1/16"–1.5" in 1/64 increments
- •Lathe/mill cutting depths often specified in thousandths (0.001")
- •Tap drill sizes
- •Standard hex bolt widths: 1/4-20, 5/16-18, 3/8-16, 1/2-13
- •Nut driver sizes: 3/8", 7/16", 1/2"
Automotive & Marine
- •Wrench sizes: 1/4", 5/16", 3/8", 7/16", 1/2", 9/16", 5/8", 11/16", 3/4"
- •Spark plug socket: 5/8" or 13/16"
- •Lug nut socket: 3/4" or 13/16"
- •Marine: keel thickness in fractional inches
- •Boat beam and draft in feet-inches
Measurement Best Practices
Reading Fractional Measurements
- •Identify the smallest graduation on your tape/ruler
- •Count numerator over denominator carefully
- •Always double-check with a second measurement
- •For precision work use vernier calipers (reads to 1/128" or 0.001")
- •Mark and measure twice before cutting
Avoiding Common Errors
- •Misreading 3/8 as 1/2 (common error)
- •Forgetting nominal vs. actual lumber/pipe sizes
- •Mixing decimal inches with fractional inches in calculations
- •Rounding 1/64" fractions to nearest 1/32"
- •Converting mm to fractional inches — remember 1 mm ≈ 3/64 inch (use calculator)
Fractional Inch Examples by Trade
Carpentry & Woodworking
- •Door gap: 1/8" around perimeter
- •Shelf thickness: 3/4" plywood
- •Dado depth: 3/8" for 3/4" shelf
- •Dowel diameter: 3/8" or 1/2"
- •Cabinet door reveal: 1/8"
- •Miter saw cut: 7/64" kerf
- •Sandpaper gap: 1/32" between sheets
Plumbing & Piping
- •1/2" copper pipe (OD: 5/8") carries typical household water
- •3/4" supply line main
- •1-1/2" P-trap drain
- •2" branch drain line
- •3" or 4" main drain
- •1/4" flare fitting for gas
- •5/8" OD refrigerant line (large)
Fasteners & Hardware
- •1/4-20 bolt: 1/4" diameter, 20 TPI
- •3/8-16 bolt: 3/8" × 16 TPI
- •#8 wood screw: 0.164" diameter
- •1/2" shank drill bit
- •6d nail: 2" long (pennyweight)
- •Drywall screw: 1-5/8" typical
- •Toggle bolt: 1/4" or 5/16" diameter
Frequently Asked Questions
What is a fractional inch?▾
A fractional inch is a measurement expressed as a fraction of one inch — for example, 1/2", 3/8", or 5/16". The fractional system is based on repeatedly halving: each level of precision doubles the denominator (1/2 → 1/4 → 1/8 → 1/16 → 1/32 → 1/64). It is the standard in US and UK trades such as carpentry, plumbing, and machining.
How do I convert decimal inches to fractions?▾
Multiply the decimal portion by the desired denominator, round to the nearest whole number, then simplify. For example, to convert 0.625" to 16ths: 0.625 × 16 = 10 → 10/16 = 5/8". So 0.625" = 5/8". For 32nds: 0.625 × 32 = 20 → 20/32 = 5/8" (same result). Our converter handles this automatically.
Why do lumber sizes not match their names?▾
Lumber is sold by nominal size (the rough-cut dimension before drying and planing), but the actual dimension is smaller. A "2×4" is actually 1.5" × 3.5" (38 mm × 89 mm). This has been the industry standard since the early 20th century. Always use actual dimensions when calculating material needs.
How accurate is a standard tape measure?▾
Most consumer tape measures are graduated to 1/16" (about 1.59 mm). Professional contractor tapes often show 1/32" marks near the end. The hook at the end has intentional play equal to the hook's thickness to compensate for inside vs. outside measurements. For precision better than 1/32", use digital calipers.
What is the difference between nominal and actual pipe size?▾
Pipe is sized by its nominal (named) diameter, which does not match the actual outside or inside diameter. For example, 1/2" copper pipe has an OD of 5/8" (0.625"). The nominal size historically referred to the approximate inside diameter of older iron pipe. Today it is simply a trade name. Always check specifications for actual dimensions when designing plumbing systems.
How do I convert inches to millimeters?▾
Multiply the inch value by 25.4. This is exact by international definition (since 1959). Examples: 1" = 25.4 mm; 1/2" = 12.7 mm; 3/4" = 19.05 mm; 1/8" = 3.175 mm. To go the other way, divide millimeters by 25.4. Our converter performs both directions instantly.