Workshop & Hardware
What Size Is My Drill Bit?
Compare a stationary bit against actual-size circles to find the closest standard diameter when the size marking is worn or missing.
Confirm calibration
Calibrate your display for best accuracy before comparing objects.
Compare the bit shaft
Remove the drill bit from the drill before measuring. Handle sharp bits carefully and compare only a stationary bit. Prefer the smooth shank when possible, not the cutting tip.
Compare two drill diameters— side-by-side or overlay
Difference highlight uses calibrated --px-per-mm. Solid = A, dashed = B in overlay.
Can't find what you're measuring?
Drill Bit Size Chart
Metric sizes are shown with the nearest fractional inch size for reference. When values differ, the conversion is approximate, not exact.
| Metric | Nearest fractional | Difference |
|---|---|---|
| 1.5 mm | 1/16" (1.59 mm) | ±0.09 mm |
| 2 mm | 5/64" (1.98 mm) | ≈ match |
| 2.5 mm | 3/32" (2.38 mm) | ±0.12 mm |
| 3 mm | 1/8" (3.17 mm) | ±0.17 mm |
| 3.5 mm | 9/64" (3.57 mm) | ±0.07 mm |
| 4 mm | 5/32" (3.97 mm) | ≈ match |
| 4.5 mm | 11/64" (4.37 mm) | ±0.13 mm |
| 5 mm | 13/64" (5.16 mm) | ±0.16 mm |
| 5.5 mm | 7/32" (5.56 mm) | ±0.06 mm |
| 6 mm | 15/64" (5.95 mm) | ≈ match |
| 6.5 mm | 1/4" (6.35 mm) | ±0.15 mm |
| 7 mm | 9/32" (7.14 mm) | ±0.14 mm |
| 7.5 mm | 19/64" (7.54 mm) | ≈ match |
| 8 mm | 5/16" (7.94 mm) | ±0.06 mm |
| 8.5 mm | 21/64" (8.33 mm) | ±0.17 mm |
| 9 mm | 23/64" (9.13 mm) | ±0.13 mm |
| 9.5 mm | 3/8" (9.53 mm) | ≈ match |
| 10 mm | 25/64" (9.92 mm) | ±0.08 mm |
| 11 mm | 7/16" (11.11 mm) | ±0.11 mm |
| 12 mm | 15/32" (11.91 mm) | ±0.09 mm |
| 13 mm | 1/2" (12.70 mm) | ±0.30 mm |
Fractional sizes follow ANSI/ASME B94.11M inch diameters (× 25.4 for mm). Number and letter drill series can be added later. Closest standard size — calibrate for best accuracy.
Common questions
How do I identify an unmarked drill bit?
Calibrate your screen and compare a stationary bit against actual-size circles to find the closest metric or fractional-inch diameter. Prefer the smooth shank when the cutting flutes are hard to align.
Do I measure the shank or the cutting diameter?
For size identification, compare the cutting diameter (or a consistent round section of the bit). Reduced-shank bits have a smaller shank than the cutting diameter—do not use the reduced shank as the size.
What fractional drill bit is closest to 5 mm?
In this chart, 5.0 mm is closest to 13/64" (about 5.16 mm). The difference is small for rough work but matters for precision fits—use the metric 5 mm bit when you need that exact size.
Are metric and fractional drill sizes interchangeable?
Not exactly. The chart shows the nearest fractional size for reference. When values differ, treat the conversion as approximate and pick the series that matches your project.
Is it safe to put a drill bit against my screen?
Only with the bit stationary and handled carefully. Do not spin the bit near the display. Prefer light contact or near-alignment; protect the screen from sharp edges and metal filings.
Are number and letter drill series included?
Not in this version. Metric and fractional-inch diameters are covered; number and letter series can be added later.