Drill chuck sizes explained
Chuck size is the largest bit shank the drill can grip, nothing more and nothing less. A 13mm chuck does not make a drill more powerful; it makes it able to hold bigger bits. The number is a capacity limit, quoted in millimeters in Europe and inches in North America for the same physical hardware: 13mm and 1/2 inch are the same chuck, 10mm and 3/8 inch are the same chuck. Here is the full size chart, what each size is for, why 13mm is the line most buyers actually care about, and how the verified chuck sizes in our 31-model dataset sort across the classes.
The mm and inch chart
| Metric | Imperial | Typical grip range | Where you find it | What it is for |
|---|---|---|---|---|
| 6.5 mm | 1/4 in | 0.5 to 6.5 mm | Light duty tools, rotary tools, small corded drills | Small holes, light gauge work |
| 8 mm | 5/16 in | 0.5 to 8 mm | Compact cordless screwdrivers, entry corded drills | Screwdriving, small bits |
| 10 mm | 3/8 in | 1 to 10 mm (often 1.5 to 10) | Homeowner cordless drills, 12V class | General home drilling and driving |
| 13 mm | 1/2 in | 1.5 to 13 mm (often 1.5 to 13) | 18V/20V cordless drill drivers, pro corded drills | Full-size bits, hole saws, spade bits, mixing paddles |
| 16 mm | 5/8 in | 3 to 16 mm | Heavy duty corded drills, high torque applications | Large bits, stirrers, industrial work |
| 20 mm | 3/4 in | 3 to 20 mm | Industrial corded drills | Very large bits |
Chart basis: Mech Forged drill chuck sizes guide; Baumarkt wissen drill chuck lexicon (capacity ranges 0.5-10 / 1.5-13 / 3-16 mm); DrillAce chuck guide; Yard and Garden Guru chuck key chart.
The grip range is the honest fine print: every chuck also has a minimum diameter below which the jaws cannot close far enough to grip. A 13mm chuck's range typically starts around 1.5mm, which in practice covers every common bit.
What 13mm actually means
Thirteen millimeters is the dividing line of the modern cordless drill market, because it is the largest chuck that fits the tool class. Two practical things follow. First, a 13mm (1/2 inch) chuck accepts full-size twist bits, large spade bits, most hole saws, and mixing paddles, all of which come with shanks that a 10mm chuck physically cannot close around at the top end. Second, buying bigger bits than your chuck holds is a real trap: the hole saw is rated by its cutter diameter, but what matters for fit is its shank or arbor. DrillAce's guide and the Mech Forged chart both make the same point: the 13mm class is what lets a drill be a general-purpose tool rather than a screwdriver with delusions.
What 13mm does not mean: power. Chuck size correlates with tool class (13mm chucks sit on the bigger, stronger platforms) but the chuck itself is a clamp, not a motor. A weak drill with a 13mm chuck still stalls on a 1 inch spade bit; the verified torque figures for judging that are in our comparison table and explained in specs explained.
10mm vs 13mm: what the difference costs you
For drilling wood up to 10mm, driving screws, and the general run of home tasks, the two sizes are interchangeable; the 10mm tool is usually lighter and often cheaper. The 13mm chuck earns its keep the day you need a 1/2 inch or larger twist bit, a big spade bit for running cable through studs, a hole saw for door locks or lights, or a paint mixing paddle. Mech Forged's sizing summary and DrillAce's consumer-guide section land on the same recommendation: 10mm (3/8 inch) covers standard homeowner duty, 13mm (1/2 inch) is the general-purpose and heavy-duty standard.
Keyed vs keyless chucks
Size and actuation are separate axes. A keyed chuck tightens with a gear tooth key for maximum grip on large bits; a keyless chuck tightens by hand, one- or two-sleeve, and dominates modern cordless drills for speed of bit changes. The tradeoff documented in the Yukiwa Seiko chuck FAQ and the ek.ua chuck comparison: keyless is convenient and fine for typical cordless torque, but grips less securely at the extreme diameters and wears eventually, while keyed holds hardest but means keeping track of the key. A ratcheting single-sleeve keyless chuck, what every 18V/20V model in our dataset uses, is the current practical answer.
Where SDS fits
SDS is a different chuck system, not a bigger version of this one. Instead of three jaws closing on a round shank, an SDS chuck locks a slotted shank with balls or rollers, so it can hold under the percussive blows of a rotary hammer; the ek.ua comparison explains why jaw chucks do not survive that duty above about 16mm. If your work is repeated holes in concrete, the answer is not a bigger keyed chuck, it is the SDS platform; our hammer drill vs rotary hammer section and the concrete picks page draw that line with the dataset's BPM figures.
Chuck sizes in our dataset
The site's 31-model dataset carries a verified chuck column, filled only where the size is confirmed to the 2-source standard; every other row is honestly blank. The verified rows so far:
| Model | Chuck | Class |
|---|---|---|
| Bosch PS31-2A (12V Max) | 3/8 in (10 mm) | 12V compact drill driver |
| Skil DL6290A-11 (PWRCore 12V) | 1/2 in (13 mm) | 12V compact drill driver |
Sourced per the dataset: Bosch PS31-2A product page and Acme Tools listing; Skil DL6290A-11 product page and Toolstash hands-on review.
Those two rows are a useful calibration: chuck size does not even track voltage within a class. The 12V Bosch carries the 10mm chuck and the 12V Skil carries the 13mm chuck, both compacts, both light duty platforms. Every 18V/20V class model in the dataset where the chuck has been confirmed so far is the 13mm (1/2 in) standard for its class. Sorting by what you can clamp, versus what the motor can turn, is exactly the split between this page and the torque discussion in specs explained.
Adapters and limits
Reducing adapters (a 13mm chuck's arbor stepped to hold small shanks) are cheap and harmless; enlarging past your chuck is not possible with an adapter. A hex-to-3-jaw adapter turns an impact driver's collet into a small chuck, but only for light duty, a limitation of the impact mechanism rather than the chuck, covered with the rest of the impact-vs-drill bit compatibility in drill bits by material. Runout, the tiny wobble of a bit spinning slightly off center, matters only for precision metal work; DrillAce's runout section is a fair summary of when it is irrelevant (hanging shelves) and when it is not (fine metalwork).
Lost the chuck key? Sizing a replacement
Keyed chucks need their key, and the key is sized by two measurements: the pilot, the pin that inserts into the hole on the side of the chuck, and the gear that meshes with the chuck's toothed ring [1] [2]. There is no single universal standard, but the industry has converged on the Jacobs K-series numbering, and most chucks carry a stamp (K1, K2, K3, or a Jacobs taper mark like JT33) that maps directly to the replacement key [1] [2].
| Key series | Pilot diameter | Typical chuck | Sources |
|---|---|---|---|
| K1 | 1/8 in (about 3.2 mm) | 1/4 in chucks | [1] [2] |
| K2 / K7 variants | 1/4 in class (7/32 to 1/4 in) | 3/8 in chucks | [1] [3] |
| K3 / K32 / KR variants | 5/16 to 11/32 in | 1/2 in chucks | [1] [3] |
Sources for this section: Zoro/Jacobs chuck key selection guide (PDF) and the same Jacobs chart mirrored at UKWorkshop (PDF); EngineerFix on measuring pilot and pinion diameters and ICS Cutting Tools' chuck key chart (pilot shank sizes K0 5/32 in through K4 3/8 in, item CK-TK series).
No stamp and no key? Measure the hole on the side of the chuck (the pilot hole) and the distance across the gear socket with calipers, and match those two numbers against a Jacobs cross-reference chart [2] [3]. Four-way universal keys cover the common residential sizes but skip industrial and proprietary variations, and a wrong-size key rounds off the chuck's gear ring permanently [2] [3]. Or sidestep the question: keyless chucks, the 13mm ratcheting sort on most modern drill drivers, need no key at all. And when the accessory you are mounting is a hole saw, the arbor shank is what the chuck actually holds; see the hole saw arbor size chart for shank and thread fit.
Quick answers
- Is 13mm better than 10mm? Not better, bigger. Same performance on everything up to 10mm shanks; the 13mm chuck additionally holds large bits and accessories.
- What does 13mm mean on a drill? The maximum bit shank diameter the jaws can close around, equivalent to 1/2 inch.
- Do I need 13mm? If you anticipate hole saws, spade bits above 10mm, or mixing paddles, yes. Screws and small holes only, no.
- Can I drill a 20mm hole with a 13mm chuck? Yes, with a hole saw or a reduced-shank bit, because the shank is what the chuck holds, not the cutting diameter.
Related guides
Also on this site: drill torque settings explained for what to do with the chuck once it holds a bit, screwdriver bit types and sizes for the driver bits a smaller chuck also has to hold, and the best hammer drills for concrete. For sizing the holes themselves, see the pilot hole chart and the tap and drill size chart.