Socket Size Chart: SAE & Metric (in Order) + Drive Sizes

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A socket size chart lists every common SAE (inch) and metric socket in order, with the exact conversion between them. SAE sockets run in 1/32- and 1/16-inch steps (1/4", 5/16", 3/8", 7/16", 1/2"...), metric sockets run in 1 mm steps (8, 9, 10, 11, 12 mm...), and 1 inch equals exactly 25.4 mm.

Only a handful of SAE and metric pairs are close enough to swap: 5/16" and 8 mm, 3/4" and 19 mm, 1-1/16" and 27 mm are the main ones. Everything else is off by enough to round a tight fastener, which is why a car with metric bolts needs metric sockets.

How to Read This Socket Size Chart

Every number below is calculated from 1 in = 25.4 mm and rounded to two decimals. The "Difference" column shows how far apart the two sockets are. In the SAE chart, a plus sign means the metric socket is larger; in the metric chart, a plus sign means the SAE socket is larger.

Our "Swap?" column uses a simple rule. Under 0.10 mm apart, the two are close enough to use in a pinch on a fastener that isn't torqued hard. Between 0.10 and 0.15 mm, the pair is close but not ideal: it may work on a loose fastener, but don't count on it. Over that, use the right socket.

One practical detail: a socket that is slightly larger than the fastener will slip on with a bit of play. A socket that is slightly smaller may not go on at all, or will need to be tapped on, which is a sign you're about to damage something.

SAE Socket Sizes in Order (With Metric Equivalents)

These are the SAE sizes you'll find in mainstream 1/4", 3/8" and 1/2" drive sets, smallest to largest.

Large SAE Sockets (Mostly 3/4" Drive)

Above 1-1/2", you're usually in 3/4" drive territory: truck hubs, axle nuts, heavy equipment. Mainstream 3/4" drive impact sets, such as GearWrench's 29-piece SAE set, run from 3/4" all the way to 2-1/2" (63.50 mm).

Metric Socket Sizes in Order (With SAE Equivalents)

Metric sockets go up in 1 mm steps. A good 1/4" drive set adds 5.5 mm, which you'll meet on small trim screws and some electrical hardware. Sizes above 24 mm thin out quickly in hand-tool sets and live mostly in 1/2" and 3/4" impact sets.

The Pairs People Get Wrong

Three near-miss swaps account for a large share of the rounded bolts owners complain about on forums:

• 13 mm and 1/2": 0.30 mm apart. A 13 mm socket on a 1/2" nut feels like it fits, then slips under load.
• 10 mm and 3/8": 0.48 mm apart, and the 3/8" is the smaller one. It won't go on a 10 mm head, so people grab 7/16" (11.11 mm) instead, which is more than a millimeter oversize.
• 17 mm and 11/16": 0.46 mm apart. Close enough to fool you, loose enough to strip corners.

If the fastener is rusted, torqued to spec or holding a brake, steering or suspension part, don't swap at all. A dedicated metric or SAE socket is cheap compared with an extractor set and a lost afternoon. Our SAE vs metric socket guide covers which system your vehicle actually uses.

Socket Drive Sizes Explained

The drive size is the square hole on the back of the socket, and it has to match your ratchet. It has nothing to do with the fastener size. Four drive sizes cover almost everything you'll do at home:

The ranges above come from current sets on the market, not from a standard, so treat them as typical. For example, GearWrench's 51-piece 1/4" drive set (80300) covers 3/16" to 9/16" and 4 to 15 mm, its 57-piece 3/8" set (80550) covers 1/4" to 1" and 6 to 19 mm, and its 1/2" drive impact sets reach 1-1/2" and 36 mm. A 1" drive also exists for heavy trucks and industrial work; GearWrench's 1" impact line, for instance, runs from 3/4" up to 4-1/2".

1/4 Socket Set: When You Need It

A 1/4" drive set is the precision tool. The small ratchet head fits behind dashboards and around sensors, and the short handle stops you from overtightening small bolts. It tops out around 9/16" and 14 to 15 mm, so it can't replace a 3/8" set.

3/8 Socket Set: The One to Buy First

If you buy one drive size, buy 3/8". It covers the 8, 10, 12, 13, 14 and 17 mm fasteners that make up most of a modern engine bay, and the ratchet is strong enough for brake caliper bolts. Look for a set that runs to at least 19 mm without skipping sizes. Our best socket set picks list exact ranges for each set.

1/2 Socket Set: For Leverage and Big Fasteners

A 1/2" drive handles lug nuts, suspension bolts and anything that needs a breaker bar. It's also the standard for impact wrenches, which is why most impact socket sets are 1/2" drive. Plan on owning one as soon as you do your own tire rotations or brake jobs.

3/4" Drive: Only for Heavy Work

You don't need 3/4" drive for a passenger car. It earns its keep on trucks, tractors and equipment where fasteners go past 1-1/2" or 38 mm. See our guide to the best 3/4" drive socket sets if that's your world.

Common Socket Sizes on Cars

Exact sizes vary by vehicle, so check a repair manual before buying single sockets. These show up again and again:

• 10 mm: the most common bolt on many modern cars (battery terminals, covers, brackets). Owners lose these sockets so often it's a running joke.
• 8, 12, 13, 14 mm: sensors, intake parts, accessory brackets.
• 15, 17, 19 mm: brake caliper bolts and brackets, suspension parts, many lug nuts.
• 21 and 22 mm: lug nuts on many cars and trucks.
• 3/4", 13/16" and 7/8": common lug nut sizes on older domestic vehicles and many trucks.
• 5/8" and 13/16": the two classic spark plug socket sizes, which is why most mechanics sets include both.

How to Find the Right Socket Size

1. Check whether the fastener is SAE or metric. Most cars built in the last few decades are largely metric, even domestic brands. Older American vehicles, lawn equipment and some trailers still use SAE.
2. Read the head if you can. Many bolts have a strength grade on the head, not the size, so don't confuse the two.
3. Measure across the flats. Use a caliper on two opposite flat sides of the hex, not corner to corner. A reading near 12.7 mm is a 1/2" head; 13.0 mm is a 13 mm head.
4. Match the reading to the chart. Find the closest size above. If the reading sits between two sizes, the fastener may be worn; try the smaller socket first.
5. Test the fit. The right socket slides on fully with almost no rotational play. If it wobbles noticeably, go down a size or switch systems.
6. Pick the right length and point count. Use a deep socket for nuts on long studs, and a 6-point socket for tight or rusty fasteners.

6-Point vs 12-Point, Deep vs Shallow

A 6-point socket grips the flats of the hex and is far less likely to round a stubborn bolt. A 12-point socket is easier to engage in tight spots because it fits on in twice as many positions, and it's required on 12-point fasteners. For general car work, start with 6-point sockets. We break this down further in our 6-point vs 12-point guide.

Shallow (standard) sockets give you clearance in tight spaces. Deep sockets reach nuts threaded far down a stud, like exhaust hardware or shock mounts. A good set includes both for every size from 10 to 19 mm.

How Sockets Are Marked

Most brands stamp or laser-etch the size on the socket's side. SAE sockets are marked in fractions (9/16) and metric sockets in millimeters (14MM or 14). Some brands add color bands or "SAE"/"MM" markings, which helps if you keep both systems in one drawer.

Common Mistakes

• Using the "close" size on a tight fastener. 13 mm on a 1/2" bolt is the classic. It works until it doesn't.
• Assuming a domestic car is SAE. Most modern vehicles from US brands are largely metric.
• Measuring corner to corner. The size is always across the flats.
• Buying a set with gaps. Some budget sets skip 16, 18 or 20 mm, or 13/16". Check the size list before you buy.
• Putting chrome sockets on an impact wrench. Use impact-rated (usually Cr-Mo, black-finish) sockets on impact guns, as tool makers specify; chrome hand sockets aren't built for repeated hammering.
• Confusing drive size with socket size. A "1/2-inch socket" can mean a 1/2" drive socket or a socket for a 1/2" bolt head. When shopping, check both.

FAQ

Next Steps

If your current set is missing sizes from the charts above, our best socket set roundup lists the full size range for every pick, and our best mechanic tool set guide covers complete kits with wrenches included.