Wrench Size Chart: SAE and Metric Sizes with Conversion Table (Free PDF)

The table above show the regular sized SAE wrenches from 1/8 in through 2-1/2 in listed by there actual decimal size. Find your wrench size in the left-most column and read across, you will find its exact decimal size and its metric equivalent. You will also see how commonly that size will be found in a combination set.

The size written on the wrench is called the width across flats (A/F). It’s the distance from one flat to another in the jaws of the wrench; this is also the same as the distance across the flats of the hex it fits.

The first column of figures is the SAE wrench size and will indicate what's stamped on the wrench as the fractional inch. The second column is the decimal version of that same size expressed to four decimal digits. Why? If you're measuring one of those oddball sizes with calipers or comparing your sizes you want to know it precisely.

The third column is the absolute conversion to mm where 25.4 mm = 1 inch. It's not a number rounded for shop use. The final column is the rarity rating of the size, it shows if the size is found commonly in standard, large, or ignition sets, or if it is rare for older equipment.

Don’t confuse wrench size with bolt size. For example, a 7/16 in wrench is not used on a 7/16 in bolt. That’s for the head of a 1/4 in bolt. The head of a 7/16 in bolt take a 5/8 in wrench.

If you’re given a thread diameter from a chart, then you need to convert that to a wrench size. To do that, you can refers to the bolt and nut quick reference table below.

Don’t mistake a metric fastener for an odd SAE size such as 13/64 in or 17/64 in because they don’t have anything to do with each other. Those are sizes that was created for ignition wrenches. You’ll hardly ever encounter a fastener requiring one of those sizes.

When measuring a worn fastener, you measure across the flats. Do not measure across the corners. Across the corners, a hex will read about 15 percent bigger then its actual size. So a 1/2 in head (0.750 in A/F) will read like 0.87 in approximately.

This means that you go down the wrong row in the table. If it's between two rows then it was probably metric, worn, or another standard.

These are box end, open end, and combination wrenches in inches only. For metric wrenches you go to the next table. If you know the size of a bolt or nut, then the quick reference table below is the one you use to match it with the right size wrench.

Then there’s the socket size chart for socket drive sizes. When it comes to Whitworth and BSF spanners they’re sized by thread size not across their flats. This is covered in detail on the spanner size chart, and you should of checked it first.

So, here’s a chart with metric wrenches listed from 4 mm up to 65 mm, in ascending order. Down the first column are standard metric wrenches by size; that is, the measurement of how wide the opening on the wrench is (across the flats). That is measured in millimetres, which is the same as what will be stamped on the wrench. And it’s the same as across-flats measurement on whatever hex it fits.

Just look at the first column where you’ll see your wrench. Read across for availability and inch equivalents.

Divide by 25.4 to get decimal inch. Use four decimal places to compare with calipers or inch tools.

Rounded to nearest 64th means it is rounded from the decimal above to the nearest 64th of an inch (Nearest 64th (in)). Good for finding your way back to an inch-marked wrench roll, or if all you have are fractions. It is not a get-out-of-jail free card to swap tools. 64th is bigger than .015 in. A fastener will round under a wrench that is even that much to big.

What is in typical sets? This refers to what manufacturers includes in combination sets. The standard size range are 8 to 19 mm. Expanded sets include 6, 7, and 20-32 mm.

Note that set makers often omit 23, 25, 26, 28, 29 & 31 mm. These are all sizes where few fastener are used. That’s the primary trap. Set makers hop over skipped sizes that don’t match the ISO fastener across-flats series. It is normal for your set to lack 23 or 29 mm. It is not a defect.

There is also the opposite trap. A 23-mm nut might realy be a worn 24 mm. Or maybe it’s an oversized 7/8 in (22.23 mm). Perhaps it’s 29/32 in. Measure carefuly before you force a wrench.

This is partly because of legacy DIN bolt heads in these sizes: 17, 19, 22, and 32 mm.

These tools does double duty on Japanese vehicles made to the JIS small head standard, using sizes 12, 14, 17, and 19 mm.

Check out the bolt and nut quick reference table for the details.

You’re out of set territory above 32 mm. Next up is the ISO across-flats series: 34, 36, 41, 46, 50, 55, 60, and 65 mm. These is all for M22 to M42 fasteners. You usually purchase them as separate ring, slogging, or open end wrench.

Between sizes, there are 33, 35, 38, 39, and 40 mm mostly for machinery, axle nuts, and pipe fittings. Before you order, make sure you know what it is that you need to turn in.

It’s a metric-marked wrench-only table. The interchange table below show when you can substitute a metric wrench for an SAE wrench. Don’t eye-ball the decimals. Direction matters. Looser = bigger; Tighter = no go. You should of checked the decimals.

Here's a table that cross references all the metric vs. SAE wrenches that can, or cannot, replace each other. It also indicates which ones is close but look like they're a replacement when they aren't. This way you can see what wrench would replace another one and it does this by pairing them with the closest metric wrench.

Then it shows the two wrenches in decimal form and then gives the difference between the two in thousandths of an inch. From there, it says if that difference are acceptable.

Less than .004 is good to go at normal torque levels. .004-.010 is ok if used carefuly at lower torques. .010-.015 will round out edges under load. Over .015 and they shouldn't be used together.

But also notice that the order matter. That's the direction of the fit. The "larger of pair" column lets you know which wrench is actualy larger. The large one goes on the small one's fastener. The large one fits loosely, the small one won't fit at all.

Like this: a 13 mm wrench will slip loosely over a 1/2 inch nut. A 1/2 inch wrench will not fit onto a 13 mm nut. If the verdict reads "usable with care," then you have to use the larger wrench on the smaller fastener. Fully seat the wrench. Use moderate torque. And do so on a fastener you can afford to mark.

Some of those swaps are truly safe to commit to memory. Those under 0.004 inches include: 5/16 inch and 8 mm, 3/4 inch and 19 mm, 1-1/16 inch and 27 mm, 29/32 inch and 23 mm, 1-13/16 inch and 46 mm, 1-1/2 inch and 38 mm, and 1-3/8 inch and 35 mm.

These are pairs that are close but not really close enough. Here the pair 1/2 inch = 13 mm is actualy 0.012 inches loose. This is a common pair that will round.

Next up, the pair 9/16 inch = 14 mm is actualy 0.011 inches loose. It's another common pair that rounds pretty consistently. And finally, the pair 3/8 inch = 10 mm is actualy 0.019 inches off. That's a rounded fastener waiting to happen. It's also a pair that confuse people frequently.

There is no usable metric partner for the 11/16 inch or the 1 inch sizes. The size 10 mm have no usable SAE partner.

The judgments apply to a new and good hex. These verdicts assume a fresh hex in good condition and a properly seated wrench. Give each judgment down a notch if the fastener is painted, plated, already marked, or rusted.

Better to use a 6-point box end wrench. It holds the flat surfaces instead of the corners. Fasteners made of stainless and chrome plate is especially prone to marking up.

This table should not be used for applications where torque is critical. For that you’ll want a socket or correct-system wrench for head bolts, flange joints, structural joints and brake hardware. You should of used one for that.

Whitworth spanners has their own system of measurement, marked with thread sizes, not across-flats. A 3/16 W spanner is certainly not 3/16 inch across flats. See our spanner size chart for those.

Use this table when you know the fastener and need the wrench. If you do know the fastener, and want to figure out the wrench, look up the fastener thread size (the first column). It will list the nominal thread diameter, e.g., 1/2 in or M10. That ain’t the wrench size!

Look across for the wrench size that fits the hex bolt head and the hex nut, though they don't always takes the same one. The final two columns is two commonly used exceptions. This chart applies to hex bolts and cap screws per ASME B18.2.1 and metric bolts per ISO 4014/4017. It also applies to finished nuts per ASME B18.2.2 and metric nuts per ISO 4032.

Bolt heads and nuts typically requires the same size wrench on the inch side, although it's not always that way. A 7/16 in. bolt head require a 5/8 in. wrench, and its nut is 11/16 in. A 9/16 in. bolt head requires a 13/16 in. wrench and its nut requires a 7/8 in. wrench. A 1-3/8 in head is 2 in and its nut is 2-1/16 in.

Heavy hex covers nuts and bolts of this pattern which is heavier. They are 1/8 in larger across the flats than standard and the same thread. These are used as structural bolting with heavy hex heads. This means a 3/4 in structural bolt will require a 1-1/4 in wrench vs. 1-1/8 in.

The metric size on the other end: One wrench fits both sides of the joint, since nuts and bolt head have matching threads (ISO). There are regional and historical exceptions. DIN legacy heads was a little bigger, M10, M12 and M14. Rather than 16, 18 and 21 mm they was 17, 19 and 22 mm. And a bit smaller too, M22 was 32 mm different than 34 mm.

You’ll see them on older European machinery, particularly trailers and agricultural equipment, as well as on some older German machines. Which explains why 17, 19 and 22 mm are kept alive in sets. Small JIS heads is common on Japanese gear and vehicles. In the M8 to M12 range, they’re one step smaller than ISO. This means an M8 is 12 mm instead of 13 mm. An M10 is 14 mm; an M12 is 17 mm. So if you’ve got a flange bolt on a Japanese M8 and your 13 mm wrench sits flopping around, this column’s why.

Wheel hardware, such as small-head cap screws and flange bolts, can differs by the manufacturer. In fact automotive fasteners does. They combine JIS, ISO & their own propriatary head styles on the same car.

If you don’t know the measurement across the flats. Rather than rely off the thread size. Grab a wrench from the run tables above.

This is a handy guide to wrenched hex heads. Should of included socket head cap screws. See our Allen key charts for that. And doesn’t include the square tapped ones. Those are covered in our spanner size chart. That chart also includes Whitworth and the full thread-to-spanner mapping.

This table tell you which pattern of a certain size to reach for. I made those tables up top telling you what wrench will fit.

So each row of the table represent a different head pattern. The Contact with fastener column tell you where on the hex the pattern sits. This determines how much torque the tool can absorbs without damaging the corner.

The "Swing to re-grip" column tell you the size of the arc you must swing before the wrench can take another bite. That is the determining factor when working in cramped pipe runs or engine bay. And finally, the last two columns explain the jobs the patterns earn and the situations where they will cause damage.

And then there’s the difference that saves your fasteners: 6-point vs. A 12-point head is used. A 6-point ring rides up on the flats. It avoids the corners, and handles high torque and a bit of wear in the hex because it never touches them.

On the other hand, a 12-point ring only touches the corners, reducing the required swing by half (to 30 degrees) while doubling the number of engagement positions. But it focus the load right at the spot where the hex first rounds off.

Practical rule: Use 6-point to break fasteners loose. Go with 6-point for those that are already damaged, soft, rusty, or otherwise problematic. Use 12-point where torque won’t be high and access is an issue.

The open end is the only one that slides on sideways into inline fittings, long studs and jam nuts. This type transmits the least amount of torque because its end grips only two flats. But since the standard open end is beveled perhaps 15 degrees away from the handle, it flips over after each stroke halving your swing, reducing your hex work from 60 to 30 degrees. That’s a trick worth practicing.

The compromise fitting for tube fittings is a flare nut wrench, which has a slot so it can go over the tubing and wraps all five flats like a ring. It’s used because open-ended wrenches tend to round off the soft brass and plated nut on fuel and brake lines. Get flare nut wrenches with 6-points where available.

Box wrenches offer ultimate strength. A ratcheting box wrench trades ultimate strength for speed; the mechanism needs only a few degrees of swing, but it has a torque limit and most are 12-point, so break the fastener loose with a solid ring first.

Adjustable wrench: This tool fits all sizes, making it a great addition to any travel kit. But its movable jaw can have play, so if using one side, seat it fully closed, load toward the fixed jaw, and never leave it on a fastener you care about.

Note that this advice refers to wrenches on hex fasteners. You can find socket-specific tools such as impact sockets, crowfoot attachments, and torque wrenches in our socket size chart.