Metric to SAE
Convert metric length measurements (mm, cm, m, km) to SAE inches and find the nearest standard fractional wrench size. Free online tool for mechanics, engineers, and DIY enthusiasts with instant, accurate results.
About This Calculator
The Metric to SAE Converter is a free online tool that instantly converts metric length measurements — millimeters (mm), centimeters (cm), meters (m), and kilometers (km) — into their SAE (Society of Automotive Engineers) equivalents in decimal inches and fractional inch sizes. Whether you are a mechanic working on an imported car, a DIY enthusiast following a US-made furniture assembly guide, an engineer collaborating on international projects, or a hobbyist in need of the right wrench size, this calculator bridges the gap between metric and SAE measurement systems.
The conversion is based on the internationally standardized inch definition: 1 inch = 25.4 millimeters (or 2.54 centimeters), established by international agreement in 1959. The calculator first converts the metric input to decimal inches using the appropriate factor — dividing millimeters by 25.4, dividing centimeters by 2.54, multiplying meters by 39.3701, or multiplying kilometers by 39,370.1. It then finds the nearest standard SAE fractional size from a comprehensive list of common wrench and bolt sizes, ranging from 1/16" to 2" in 1/16" and 1/32" increments, and reports the difference in millimeters.
In the United States, SAE sizes dominate automotive and construction industries, while metric fasteners are found in imported vehicles and modern global products. The United Kingdom uses a mixed system with metric for most official measurements but imperial for certain applications. India, while officially metric, still encounters SAE sizes in imported machinery, older equipment, and specialized tools. This converter is designed for users across all regions who need to quickly determine the closest SAE equivalent for any metric measurement.
Frequently Asked Questions
How do you convert metric sizes to SAE sizes?
To convert metric to SAE, first convert the metric measurement to inches. For millimeters, divide by 25.4. For centimeters, divide by 2.54. For meters, multiply by 39.3701. Then find the nearest standard SAE fraction from common wrench sizes like 1/4", 5/16", 3/8", 7/16", 1/2", 9/16", 5/8", 11/16", 3/4", 13/16", 7/8", and 15/16".
What is SAE measurement system?
SAE stands for Society of Automotive Engineers. The SAE measurement system is a subset of the imperial system used primarily in the United States for automotive and mechanical engineering. SAE sizes are expressed in fractional inches such as 1/4", 3/8", and 1/2", commonly used for bolts, nuts, wrenches, and mechanical fasteners.
What is 19 mm in SAE size?
19 mm converts to approximately 0.748 inches. The nearest SAE wrench size is 3/4" (0.75 inches), which is slightly larger by about 0.05 mm. In practice, a 3/4" wrench can be used on a 19 mm bolt with minimal play, though a proper 19 mm wrench is preferred for a tighter fit.
What are the most common metric to SAE conversions?
Common conversions include: 24 mm = 15/16", 22 mm = 7/8", 21 mm = 13/16", 19 mm = 3/4", 18 mm = 11/16", 16 mm = 5/8", 14 mm = 9/16", 13 mm = 1/2", 11 mm = 7/16", 10 mm = 3/8", 8 mm = 5/16", and 6 mm = 1/4". These are the most frequently encountered conversions in automotive and mechanical work.
Can you use a metric wrench on an SAE bolt?
Yes, in most cases you can use a metric wrench on an SAE bolt and vice versa since the size differences are often minimal. However, using a slightly larger wrench than needed can deform, wear, or strip a bolt head. It is always best to use the correct size wrench. Our calculator helps you find the closest match when you don't have the exact tool available.
What is the difference between SAE and metric fasteners?
SAE fasteners are measured in fractional inches (e.g., 1/4-20, 3/8-16) and are common in US-manufactured vehicles and equipment. Metric fasteners are measured in millimeters (e.g., M6, M8, M10) and are standard in most other countries including India, the UK, and Europe. Many modern vehicles use a mix of both systems, making a metric to SAE converter essential for mechanics and DIY enthusiasts.