Standing in the tool aisle with a metric bolt and a rack of SAE sockets is a frustrating way to figure out sizes. This socket size chart gives you the metric to SAE conversions in both directions, so you can grab the right socket the first time. It’s formatted to print, because the chart is most useful when it’s hanging in your shop next to the tool chest.
The first rule of socket sizing: a socket must be a fractional touch snug on the fastener head, never loose enough to round it off. The conversions below are the closest standard sizes. Metric and SAE sockets rarely match exactly, so pick the size that fits snug, not the size that’s mathematically nearest on paper.
Metric to SAE Socket Size Conversion Chart
This table runs from the smallest common sizes up through the big impact sockets. The SAE column is the closest standard fractional size to the metric size. Check the diameter column if a manufacturer calls out a size you don’t recognize.
| Metric (mm) | Closest SAE | Equivalent | Drive Size | Notes |
|---|---|---|---|---|
| 6 mm | 1/4 in. | 1/4 in. = 6.35 mm | 1/4 in. | Small screws and nuts |
| 8 mm | 5/16 in. | 5/16 in. = 7.94 mm | 1/4 in. | Common on 5.5 mm fasteners |
| 10 mm | 3/8 in. | 3/8 in. = 9.53 mm | 3/8 in. | Most common socket on a car |
| 11 mm | 7/16 in. | 7/16 in. = 11.11 mm | 3/8 in. | 10 mm bolt head with a 11 mm nut |
| 13 mm | 1/2 in. | 1/2 in. = 12.70 mm | 3/8 in. or 1/2 in. | Very common automotive size |
| 14 mm | 9/16 in. | 9/16 in. = 14.29 mm | 3/8 in. or 1/2 in. | Lug nuts often 13, 14, or 19 mm |
| 15 mm | 19/32 in. | 19/32 in. = 15.08 mm | 1/2 in. | For European cars |
| 16 mm | 5/8 in. | 5/8 in. = 15.88 mm | 1/2 in. | Common on trucks |
| 17 mm | 11/16 in. | 11/16 in. = 17.46 mm | 1/2 in. | Brake caliper bolts |
| 18 mm | 23/32 in. | 23/32 in. = 18.26 mm | 1/2 in. | Rare but shows up on imports |
| 19 mm | 3/4 in. | 3/4 in. = 19.05 mm | 1/2 in. | Lug nuts on many full-size trucks |
| 21 mm | 13/16 in. | 13/16 in. = 20.64 mm | 1/2 in. | Chevy and GMC lug nuts |
| 22 mm | 7/8 in. | 7/8 in. = 22.23 mm | 1/2 in. | Wheel and suspension work |
| 24 mm | 15/16 in. | 15/16 in. = 23.81 mm | 1/2 in. | Axle nuts and big fasteners |
| 27 mm | 1-1/16 in. | 1-1/16 in. = 26.99 mm | 1/2 in. | European axle nuts |
| 30 mm | 1-3/16 in. | 30 mm = 1.18 in. | 3/4 in. drive | Big truck and industrial work |
| 32 mm | 1-1/4 in. | 32 mm = 1.26 in. | 3/4 in. drive | Axle nuts on heavy pickups |
SAE to Metric Quick Lookup
| SAE Size | Millimeters | Closest Metric |
|---|---|---|
| 1/4 in. | 6.35 mm | 6 mm |
| 5/16 in. | 7.94 mm | 8 mm |
| 3/8 in. | 9.53 mm | 10 mm |
| 7/16 in. | 11.11 mm | 11 mm |
| 1/2 in. | 12.70 mm | 13 mm |
| 9/16 in. | 14.29 mm | 14 mm |
| 5/8 in. | 15.88 mm | 16 mm |
| 11/16 in. | 17.46 mm | 17 mm |
| 3/4 in. | 19.05 mm | 19 mm |
| 13/16 in. | 20.64 mm | 21 mm |
| 7/8 in. | 22.23 mm | 22 mm |
| 15/16 in. | 23.81 mm | 24 mm |
| 1 in. | 25.40 mm | 25 mm |
| 1-1/16 in. | 26.99 mm | 27 mm |
| 1-1/4 in. | 31.75 mm | 32 mm |
Two sockets trade places more than any other: 10 mm and 13 mm, with 19 mm close behind for trucks. If you only carry a few sockets, those three cover most underhood and undercarriage work.
Standard vs Deep vs Impact Sockets
Standard sockets reach most fasteners. Deep sockets get past studs and into recesses. Impact sockets are the thick-walled black-and-chrome ones meant for impact wrenches, chrome sockets will crack under a hammering impact gun. Use chrome sockets by hand or with a ratchet, and impact sockets with an impact driver or impact wrench.
Drive Sizes and When to Use Each
Drive size is the square socket on the ratchet itself, not the fastener. 1/4 in. drive covers small precision work, 3/8 in. is the everyday sweet spot, and 1/2 in. handles lug nuts and heavy-duty fasteners. 3/4 in. and up belong to trucks and industrial jobs. Most DIYers live on 3/8 in. with a 1/2 in. adapter for the big stuff.
Get a Complete Set of Sockets
Once you know your sizes, the smart move is a full mechanics set so you stop hunting for the one socket you need. All three sets below ship metric and SAE together and include deep and shallow sockets plus the ratchets and extensions to use them.
Complete Sockets for Every Size in the Chart
| Product | Price | Best For | Buy |
|---|---|---|---|
| DeWalt 168-Piece Mechanics Tool Set | $177.12 | Metric and SAE sockets, 1/4 and 3/8 and 1/2 drive, good for the home garage | Buy Now |
| Stanley FatMax 187-Piece Mechanics Tool Set | $179.97 | Bigger coverage of metric and SAE sizes in one case | Buy Now |
| Craftsman 230-Piece Mechanics Tool Set | $224.70 | Most complete set of the three, three-drawer case, deepest socket range | Buy Now |
Prices checked at time of writing and change without notice. See all tested mechanic tool sets →
Frequently Asked Questions
Is a 10 mm socket the same as 3/8 inch?
Close enough for most purposes but not exact. 3/8 in. equals 9.53 mm, so a 10 mm socket is the nearest metric size and a 3/8 in. SAE socket is the nearest fractional size. Whichever fits snug on the fastener is the one to use.
What size socket fits a 19 mm nut?
Use a 19 mm socket if you have it. The closest SAE equivalent is 3/4 in. (19.05 mm), which is a near-exact match and works in a pinch. Always reach for the exact size first.
Can I use metric sockets on SAE bolts?
Sometimes, but it’s never ideal. A loose socket rounds off a hex head fast. Pick the size that fits snug and use the proper hex for anything high-torque. This is why mechanics carry both metric and SAE.
What drive size do I need?
3/8 in. drive for everyday work, 1/2 in. for lug nuts and heavy fasteners, 1/4 in. for small precision jobs. If you buy a 3/8 in. drive set, a 1/2 in. adapter extends it to big sockets when you need them.
Do I need impact sockets?
Only if you use an impact wrench or impact driver on the fastener. Chrome-plated sockets crack under impact. Impact sockets are thicker walled and built for it, and they work fine with a hand ratchet too.
Are SAE and metric sockets interchangeable?
Not directly. SAE sockets measure in inches and metric sockets in millimeters. Some sizes are near matches (19 mm and 3/4 in. are within 0.05 mm), but the set of sizes each system covers differs, so most mechanics keep both rails full.
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