Metric to Standard Socket Conversion Chart & Calculator
Convert between metric (mm) and SAE (standard) socket sizes instantly. Enter any value below. Results update as you type, with no submit button.
Metric (mm) → Standard (SAE)
- Decimal
- 0.5512"
- Closest SAE
- 9/16"
- Difference
- -0.0113"
- Compatibility
- Use with Caution
Standard (SAE) → Metric (mm)
- Decimal
- 0.7500"
- Exact mm
- 19.050mm
- Closest mm
- 19mm
- Difference
- 0.050mm
What Is Metric to Standard Socket Conversion?
Metric to standard socket conversion is the process of matching a millimeter-sized socket to its closest fractional-inch (SAE) equivalent, or the reverse. Metric sockets measure the distance across their hexagonal opening in millimeters (8mm, 10mm, 13mm). SAE sockets, built to Society of Automotive Engineers (SAE) standards, measure that same opening in fractional inches (5/16 inch, 3/8 inch, 1/2 inch). The two systems never line up exactly. The inch and the millimeter are different base units, defined by separate standards bodies. One inch equals exactly 25.4mm, so dividing a millimeter size by 25.4 gives the decimal-inch equivalent, and multiplying an inch value by 25.4 gives the millimeter equivalent. A conversion chart or calculator does this arithmetic and then rounds to the nearest size a toolbox actually stocks.
Socket conversion charts solve three problems for a mechanic, technician, or engineer working across both systems. First, they save time: instead of calculating 14 ÷ 25.4 by hand, a chart shows 14mm sits closest to 9/16 inch. Second, they prevent damage: a socket that is 0.020 inch too large will round the corners off a bolt head, and a chart flags that risk before it happens. Third, they build confidence when a toolbox is missing one size, since the chart shows exactly how close a substitute really is and whether it is safe to use.
The most common use is automotive repair, where a shop might have a customer's older American vehicle built to SAE fasteners sitting next to a modern import built entirely to metric spec. Mechanics use these charts in small engine repair too (lawn equipment, generators, outboard motors), industrial maintenance, machining, and general fabrication. A socket conversion chart is equally useful for a home mechanic who owns only one socket set and needs to know if it will work on an unfamiliar bolt.
A complete socket conversion reference has four parts: a metric-to-SAE chart, a reverse SAE-to-metric chart, an interchangeability rating for every pairing (so a user knows not just the closest size but whether it is safe to use), and supporting data such as drive size, socket type (6-point, 12-point, impact, deep), and which vehicle manufacturers use which system. This page covers all four, plus a live calculator that updates as you type.
Complete Socket Size Conversion Chart: Metric (mm) to Standard (SAE)
This chart lists every common metric socket size from 3.18mm to 50mm next to its closest SAE equivalent, the exact decimal difference, and an interchangeability rating. Type a value into the filter box to jump straight to a size.
| mm | SAE | Decimal | Difference | Compatibility |
|---|---|---|---|---|
| 3.18mm | 1/8" | 0.125" | 0.000" | ✓ |
| 4mm | 5/32" | 0.156" | -0.001" | ✓ |
| 5mm | 3/16" | 0.188" | -0.009" | ~ |
| 6mm | 7/32" | 0.219" | -0.017" | ✗ |
| 7mm | 1/4" | 0.250" | -0.025" | ✗ |
| 8mm | 5/16" | 0.313" | -0.002" | ✓ |
| 9mm | 11/32" | 0.344" | -0.010" | ~ |
| 10mm | 3/8" | 0.375" | -0.019" | ✗ |
| 11mm | 7/16" | 0.438" | -0.005" | ✓ |
| 12mm | 15/32" | 0.469" | +0.003" | ✓ |
| 13mm | 1/2" | 0.500" | -0.012" | ~ |
| 14mm | 9/16" | 0.563" | -0.012" | ~ |
| 15mm | 19/32" | 0.594" | +0.003" | ✓ |
| 16mm | 5/8" | 0.625" | -0.005" | ✓ |
| 17mm | 21/32" | 0.656" | +0.013" | ~ |
| 18mm | 11/16" | 0.688" | +0.021" | ✗ |
| 19mm | 3/4" | 0.750" | -0.002" | ✓ |
| 20mm | 25/32" | 0.781" | +0.006" | ~ |
| 21mm | 13/16" | 0.813" | +0.014" | ~ |
| 22mm | 7/8" | 0.875" | -0.009" | ~ |
| 23mm | 29/32" | 0.906" | 0.000" | ✓ |
| 24mm | 15/16" | 0.938" | -0.007" | ~ |
| 25mm | 1" | 1.000" | -0.016" | ✗ |
| 27mm | 1-1/16" | 1.063" | +0.001" | ✓ |
| 28mm | 1-1/8" | 1.125" | +0.023" | ✗ |
| 30mm | 1-3/16" | 1.188" | +0.006" | ~ |
| 32mm | 1-1/4" | 1.250" | -0.010" | ~ |
| 34mm | 1-5/16" | 1.313" | -0.026" | ✗ |
| 35mm | 1-3/8" | 1.375" | +0.003" | ✓ |
| 36mm | 1-7/16" | 1.438" | +0.020" | ✗ |
| 38mm | 1-1/2" | 1.500" | +0.004" | ✓ |
| 41mm | 1-5/8" | 1.625" | +0.011" | ~ |
| 46mm | 1-13/16" | 1.813" | +0.001" | ✓ |
| 50mm | 2" | 2.000" | +0.032" | ✗ |
Legend: ✓ Highly Interchangeable (diff ≤ ±0.005") | ~ Use with Caution (diff ≤ ±0.015") | ✗ Not Recommended (diff > ±0.015")
How to Convert Metric Sockets to Standard (SAE)
Metric → Standard
Standard → Metric
Fraction → Decimal
Detailed Conversion Examples
Example 1: Converting 14mm to Standard
- Start with the 14mm metric socket size.
- Divide by 25.4: 14 ÷ 25.4 = 0.5512 inches.
- Find the closest standard fraction: 9/16" = 0.5625".
- Calculate the difference: 0.5625" − 0.5512" = 0.0113" larger.
Result: 14mm is closest to 9/16" SAE. The gap is 0.011", so use it with caution on tight or torque-critical fits.
Example 2: Converting 3/4" to Metric
- Start with the 3/4" standard socket size.
- Convert to decimal: 3 ÷ 4 = 0.75 inches.
- Multiply by 25.4: 0.75 × 25.4 = 19.05mm.
- Closest metric size: 19mm = 0.7480".
Result: 3/4" is closest to 19mm. The gap is only 0.002", a highly interchangeable match.
Example 3: Converting 11/16" to Metric
- Start with the 11/16" standard socket size.
- Convert to decimal: 11 ÷ 16 = 0.6875 inches.
- Multiply by 25.4: 0.6875 × 25.4 = 17.4625mm.
- Closest metric size: 17mm = 0.6693".
Result: 11/16" is closest to 17mm. The gap is 0.013", a good match for most general repair work.
Common Metric Socket Sizes in SAE: Quick Reference
What is 8mm in SAE?
8mm is closest to 5/16" (0.313"), a difference of -0.002".
What is 10mm in SAE?
10mm is closest to 3/8" (0.375"), a difference of -0.019".
What is 11mm in SAE?
11mm is closest to 7/16" (0.438"), a difference of -0.005".
What is 12mm in SAE?
12mm is closest to 15/32" (0.469"), a difference of +0.003".
What is 13mm in SAE?
13mm is closest to 1/2" (0.500"), a difference of -0.012".
What is 14mm in SAE?
14mm is closest to 9/16" (0.563"), a difference of -0.012".
What is 15mm in SAE?
15mm is closest to 19/32" (0.594"), a difference of +0.003".
What is 16mm in SAE?
16mm is closest to 5/8" (0.625"), a difference of -0.005".
What is 17mm in SAE?
17mm is closest to 21/32" (0.656"), a difference of +0.013".
What is 18mm in SAE?
18mm is closest to 11/16" (0.688"), a difference of +0.021".
What is 19mm in SAE?
19mm is closest to 3/4" (0.750"), a difference of -0.002".
What is 21mm in SAE?
21mm is closest to 13/16" (0.813"), a difference of +0.014".
What is 22mm in SAE?
22mm is closest to 7/8" (0.875"), a difference of -0.009".
What is 24mm in SAE?
24mm is closest to 15/16" (0.938"), a difference of -0.007".
What is 27mm in SAE?
27mm is closest to 1-1/16" (1.063"), a difference of +0.001".
What is 32mm in SAE?
32mm is closest to 1-1/4" (1.250"), a difference of -0.010".
What is 36mm in SAE?
36mm is closest to 1-7/16" (1.438"), a difference of +0.020".
Most Popular Metric to SAE Socket Conversions
These eight conversions cover most day-to-day automotive and workshop tasks. Keep this short list handy even if the full chart above stays in the truck.
| Metric | SAE Equivalent | Common Use | Interchangeable |
|---|---|---|---|
| 8mm | 5/16" | Small fasteners, body panels | ✓ |
| 10mm | 3/8" | Most common automotive bolt size | ~ |
| 12mm | 15/32" | Engine bay bolts | ✓ |
| 13mm | 1/2" | Spark plugs, brake calipers | ~ |
| 14mm | 9/16" | Oil drain plugs | ~ |
| 17mm | 21/32" | Lug nuts (many vehicles) | ~ |
| 19mm | 3/4" | Lug nuts, axle nuts | ✓ |
| 22mm | 7/8" | Oxygen sensors | ~ |
When Can You Use a Metric Socket on a Standard Bolt?
Highly Interchangeable (≤ ±0.005")
4mm ≈ 5/32", 8mm ≈ 5/16", 19mm ≈ 3/4", 27mm ≈ 1-1/16". Safe for general mechanical work; 6-point sockets recommended.
Use with Caution (≤ ±0.015")
10mm ≈ 3/8", 13mm ≈ 1/2", 17mm ≈ 21/32". Acceptable for hand tools on non-critical fasteners; avoid on torque-sensitive applications.
Not Recommended (> ±0.015")
6mm/7/32", 7mm/1/4", 25mm/1". High risk of rounding fastener heads. Always use the correct size.
For precision work and torque-critical applications such as cylinder head bolts, suspension components, and brake calipers, always use the exact matching socket. Soft fastener materials like brass and aluminum strip easily. Chrome vanadium 6-point sockets grip the flats of a fastener rather than the corners, which reduces rounding risk when a substitute size is unavoidable. Calibrate the torque wrench for the fastener's specified value before final tightening, since an oversized socket can slip under load even when it seats correctly by hand.
Socket Types and Size Accuracy Requirements
6-Point Sockets
A 6-point socket grips all six flats of a hex fastener at once, spreading load evenly across the head. This makes it more forgiving of a slightly mismatched size and the first choice for corroded, tight, or already-rounded fasteners.
12-Point Sockets
A 12-point socket has twice as many contact points, so it slips onto a fastener in more wrench positions, which helps in confined engine bays. That extra clearance means it grips the corners rather than the flats, so it needs a more precise size match. Cross-system use (a metric 12-point on an SAE bolt or vice versa) carries a higher rounding risk than 6-point.
Impact Sockets
Impact sockets use thicker walls and a softer, more shock-absorbing steel alloy built for the sudden torque pulses of an impact wrench. That torque arrives in hammer blows rather than steady pressure, so an exact size match matters more than with a hand tool. Never use a chrome (hand) socket on an impact wrench. Chrome sockets are hardened and brittle, and impact force can crack or shatter them.
Deep Sockets
Deep sockets use the same mm-to-SAE conversion rules as standard-length sockets. Their extra length reaches recessed fasteners: spark plugs, suspension bolts, and nuts on a long threaded stud where a standard socket would bottom out before reaching the nut.
Deep Socket Sizes →Drive Sizes
The drive size is the square peg on the ratchet end of the socket, not the hex size that grips the fastener. 1/4" drive suits small fasteners and interior trim work. 3/8" drive handles most general automotive jobs. 1/2" drive covers heavy-duty automotive and light industrial torque. 3/4" and 1" drive are reserved for industrial and heavy equipment work where torque requirements exceed what a 1/2" ratchet can safely deliver.
Drive Size Adapter →Socket Sizes by Application: Automotive, Small Engine and Heavy Equipment
Automotive Work
Metric: 8, 10, 12, 13, 14, 17, 19mm
SAE: 5/16, 3/8, 7/16, 1/2, 9/16, 5/8, 3/4"
This range covers spark plugs, brake calipers, lug nuts, axle nuts, oil drain plugs, and oxygen sensors on most cars and light trucks built since the 1980s.
Small Engine Repair
Metric: 6, 7, 8, 9, 10, 11mm
SAE: 1/4, 5/16, 3/8, 7/16"
Lawn mowers, chainsaws, generators, and outboard motors use smaller fasteners than full-size vehicles, so a compact metric set covering 6mm to 11mm handles nearly every job.
Heavy Equipment
Metric: 22, 24, 27, 30, 32, 36mm
SAE: 7/8, 15/16, 1, 1-1/8, 1-1/4, 1-1/2"
Industrial equipment, manufacturing lines, fabrication shops, and maintenance crews need the larger end of the range, since structural bolts and heavy castings use bigger fasteners than a passenger car.
How to Identify Socket Sizes
Socket sizes are stamped on the side or drive end of every socket. Metric sockets show numbers only (10, 13, 17). Standard sockets show fractions (3/8, 1/2, 5/8). When markings are worn smooth from years of use, measure the internal opening with calipers across two opposite flats, not corner to corner, since a corner-to-corner measurement reads larger than the true size. A socket size gauge, a flat plate with graduated hex cutouts, gives a fast visual match without a caliper. Some premium sockets stamp both measurements on the same face, so a single socket set doubles as a quick metric-to-SAE reference.
Metric vs SAE by Country and Region
Fastener standards follow manufacturing history more than geography. The table below shows which system dominates in six major markets and where the other system still shows up.
| Region | Primary System | Secondary System |
|---|---|---|
| United States | Standard (SAE) | Metric (increasing) |
| Europe | Metric | Rarely Standard |
| Japan | Metric | Rarely Standard |
| United Kingdom | Metric | Some older vehicles use Standard |
| Canada | Metric | Standard on US-made vehicles |
| Australia | Metric | Standard on older vehicles |
Socket Standards by Vehicle Manufacturer
Knowing a manufacturer's fastener standard narrows down which socket set to grab before opening the hood. Japanese and European brands have used metric fasteners exclusively for decades; American brands transitioned gradually between the 1970s and 1980s.
| Manufacturer | Primary System | Notes |
|---|---|---|
| Toyota, Honda, Nissan | Metric | Always metric |
| BMW, Mercedes-Benz, Volkswagen | Metric | Always metric |
| Ford | Mixed/Metric | Transitioned 1970s–1980s |
| General Motors (Chevrolet, GMC) | Mixed/Metric | Transitioned 1970s–1980s |
| Chrysler, Dodge, Jeep | Mixed/Metric | Transitioned 1970s–1980s |
| Harley-Davidson | Mixed | Some models still use Standard |
Socket Set Buying Recommendations
Beginner Set
Start with one system, not both. A basic metric set (8mm to 19mm) covers most modern vehicles; a basic SAE set (1/4" to 3/4") covers older American vehicles and general hardware. Choose 6-point sockets first, since they grip better and resist rounding while you're still learning which size fits which bolt.
Professional Set
A working mechanic needs both complete metric and SAE sets across multiple drive sizes (1/4", 3/8", 1/2"), plus both standard-length and deep sockets. Buying a matched brand set keeps tolerances consistent across the whole range, which matters more than any single size.
Specialty Needs
Add a dedicated impact socket set if you own an impact wrench. Never substitute chrome hand sockets for impact use. For damaged or rounded fasteners, a set of extraction sockets (bolt-out or similar) removes stripped bolts without drilling.
Socket Maintenance and Storage
Sockets last decades with basic care. A few habits protect both the tool and its size markings.
- Store sockets on rails or in foam trays with the size visible, so you can find one without unstacking the whole set.
- Keep metric and SAE sets in separate rows or trays. Mixing them is the single biggest cause of grabbing the wrong size under time pressure.
- Wipe sockets down after use, especially after exposure to brake cleaner, coolant, or salt, to stop corrosion from obscuring the stamped size.
- Apply a light coat of oil to chrome sockets before long-term storage to prevent surface rust.
- Check impact sockets for cracks or chips before each use. A cracked impact socket can fail suddenly under torque.
Frequently Asked Questions: Metric to Standard Socket Conversion
Can I use a metric socket on a SAE bolt?
Yes, if the size difference is 0.005 inches or less. For example, a 19mm socket works on a 3/4" bolt, since the difference is only 0.002 inches. If the difference is larger than 0.005 inches, the fit loosens enough to round the bolt head under torque, so always use the exact size for torque-critical or precision work.
What is 19mm in SAE?
19mm equals 3/4 inch (0.750 inch). The exact decimal is 0.7480 inch, a difference of only 0.002 inch, making the two sizes highly interchangeable.
What is 17mm in SAE?
17mm equals 21/32 inch (0.656 inch). The exact decimal is 0.6693 inch, a difference of 0.013 inch, so use it with caution on non-critical fasteners.
What is 10mm in SAE?
10mm equals 3/8 inch (0.375 inch). The exact decimal is 0.3937 inch, a difference of 0.019 inch, which is not recommended for precision or torque-critical work.
What is 13mm in SAE?
13mm equals 1/2 inch (0.500 inch). The exact decimal is 0.5118 inch, a difference of 0.012 inch, so use it with caution.
What is 15mm in SAE?
15mm equals 19/32 inch (0.594 inch). The exact decimal is 0.5906 inch, a difference of only 0.003 inch, making the two sizes highly interchangeable.
What size socket fits a 14mm bolt?
A 14mm bolt takes a 14mm metric socket. If only an SAE set is available, the closest size is 9/16 inch (0.5625 inch), which is 0.011 inch larger than the exact 0.5512-inch conversion, so treat it as a caution-level fit.
How do I convert mm to SAE?
Divide the millimeter value by 25.4 to get decimal inches, then match that decimal to the closest fractional size on a conversion chart. For example, 12mm ÷ 25.4 = 0.4724 inch, which is closest to 15/32 inch.
What is the difference between SAE and metric sockets?
SAE sockets are sized in fractional inches, such as 1/4, 3/8, and 1/2 inch. Metric sockets are sized in millimeters, such as 10mm, 13mm, and 17mm. The two standards were developed independently by different organizations, using different base units, so their sizes never align exactly.
Are metric and SAE socket sizes interchangeable?
Yes, for pairings with a difference of 0.005 inch or less, such as 19mm and 3/4 inch. No, for pairings with a difference above 0.015 inch, such as 25mm and 1 inch, where the loose fit rounds the fastener under torque.
Why don't metric and standard sizes match exactly?
The millimeter and the inch are unrelated base units, defined by separate standards bodies. One inch equals exactly 25.4mm, and dividing that ratio across a practical range of tool sizes produces decimal values that rarely land on a clean fractional-inch size.
Do I need both metric and standard socket sets?
Yes, if you work on vehicles or equipment from different eras and regions. Most vehicles built after the 1980s use metric fasteners exclusively, but older American vehicles, some Harley-Davidson models, and a range of industrial machinery still use SAE.
How do I know if my car uses metric or standard fasteners?
Most vehicles built after 1980, and virtually all Japanese, European, and Korean models, use metric fasteners. American vehicles built before the 1970s typically use SAE. The fastest way to confirm is to try a metric socket on an accessible bolt head, such as a wheel lug nut, or check the service manual.
What socket sizes are most commonly needed for automotive work?
The most common metric sizes are 8mm, 10mm, 12mm, 13mm, 14mm, 17mm, and 19mm. The most common SAE sizes are 5/16, 3/8, 7/16, 1/2, 9/16, 5/8, and 3/4 inch. The 10mm socket is widely reported as the most frequently lost tool in a mechanic's toolbox, since it fits so many small bolts that it gets set down and misplaced constantly.
What happens if I use the wrong size socket?
An oversized socket rounds the corners off the fastener head, which makes it slip under torque and can leave the fastener impossible to remove with a normal tool. In severe cases, removal requires a bolt extractor or drilling the head off entirely, so a size that's even 0.015 inch too large is worth avoiding.
How accurate do socket conversions need to be?
For general mechanical work, a difference of 0.005 inch or less is considered a safe substitute. For high-torque applications, precision machinery, or soft fastener materials like brass and aluminum, use the exact size rather than the closest conversion.
Can impact sockets be used with hand ratchets?
Yes, impact sockets work fine on a hand ratchet, though they're heavier and bulkier than a standard chrome socket. The reverse is not safe: a chrome hand socket can crack or shatter under an impact wrench's hammering torque.
What are deep sockets used for?
Deep sockets reach recessed fasteners, spark plugs, suspension nuts, and bolts with a long protruding shaft, where a standard-length socket would bottom out on the shaft before reaching the nut.
More Socket & Wrench Conversion Tools
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Reverse conversion from fractional inches to millimeters.
Metric and SAE bolt head, thread, and wrench sizes.
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Correct drill size for metric and SAE thread tapping.
Metric, UNC, UNF, and Whitworth thread standards.
Impact-rated socket sizes by drive size.
Deep well sockets for spark plugs and recessed fasteners.
1/4", 3/8", 1/2", 3/4" drive conversions.
Millimeter to fractional inch conversion chart.
Wrench fractions to decimal inches and mm.
Metric and SAE hex key sizes.