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US Nickel diameter
Exact matchUS 5-cent coin (exact: 21.21mm)
Coins & Currency
Conversion breakdown
21.9 mm to inches
mmtoinches.imView decimal inches, fractional inches (1/32" precision), and feet+inches for 21.9 millimeters. Perfect for CNC setups, woodworking, construction documents, and any workflow where a single metric dimension needs multiple imperial formats.
Decimal inches
0.8622"
21.9 mm = 0.8622" (rounded to four decimals)
Fractional inches (1/32")
7/8"
Error ±0.012795"
Feet + inches
0.8622"
Total inches 0.8622"
Real-world size reference
Visualize 21.9 mm with familiar everyday objects and common items for better understanding.
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M20 bolt diameter
Exact matchLarge structural fastener
Hardware & Fasteners
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US Nickel diameter
Close matchUS 5-cent coin is 21.21mm
Coins & Currency
Note about measurements
Exact matches indicate precise dimensional equivalence. Close matches show similar sizes for visual reference. Always verify exact specifications for precision work, especially in engineering, manufacturing, or construction applications.
Visual size comparison
See how 21.9 mm compares to common reference sizes
Sizes are scaled for comparison. Click "Show 1:1 actual size" above to see the true physical size.
Tip: This visualization helps you quickly understand the relative size of 21.9 mm. Toggle between scaled comparison and 1:1 actual size using the button above.
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Common questions about 21.9 mm
Quick answers to frequently asked questions about this measurement, conversions, and practical applications.
21.9 mm equals 0.8622 inches. This conversion uses the international standard where 1 inch = 25.4 millimeters exactly.
21.9 mm is approximately 7/8". Approximately 7/8", with a 0.33mm difference. Suitable for rough measurements but verify for precision work.
21.9mm is comparable to medium-sized everyday objects like coins, batteries, or small hardware items.
Use millimeters when working with metric tools, international standards, or technical specifications. Use inches for imperial-system projects, construction in the US/UK, or when collaborating with teams using imperial measurements. For precision machining, decimal inches are preferred over fractions.
Acceptable tolerance depends on your application. General woodworking: ±0.5mm is typical. Metal fabrication: ±0.1-0.3mm. Precision machining: ±0.01-0.05mm. Electronics: ±0.02mm or tighter. Always check your project specifications or industry standards.
Still have questions? Try the interactive converter for more conversion options and tools.
Related conversions
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Conversion details
All calculations rely on the international standard of 1 inch = 25.4 millimeters. Decimal values are rounded to four places, fractional results use 1/32" increments with automatic simplification, and feet+inches formatting is ideal for dimensions above 300 mm. For higher precision, URL parameters, or bulk conversion needs, head back to the main calculator or batch converter.
At 21.9 mm (~0.8622 in), This falls in a common fabrication / home‑improvement range. Use decimal inches for calculations; fractional inches aid field readability; consider adding tolerances on drawings.