Inch Converter

About the Inch Converter

The inch is a foundational unit in the US customary and imperial measurement systems. Whether you are working on a woodworking project that uses fractional inches, reading product dimensions listed in centimeters, or converting blueprint measurements to metric, you need reliable inch conversions across several target units.

The page converts inches to and from seven different length units — millimeters, centimeters, meters, feet, yards, micrometers, and miles. Choose your conversion direction, enter a value, and review results in all units simultaneously. Adjustable decimal precision lets you match the accuracy your task demands.

A built-in inch-fraction to millimeter reference table covers every common fraction from 1/64 to 1 inch, making this especially valuable for machinists, carpenters, and engineers who routinely work with fractional inch measurements. It also helps students and technicians verify conversion steps without switching between multiple separate references during shop, classroom, and field workflows.

When This Page Helps

Unlike single-direction converters, the page works bidirectionally — convert inches to centimeters or centimeters back to inches while keeping the related units visible together. That matters when a dimension needs to move between fractional-inch shop practice, decimal-inch specifications, and metric documentation. The adjustable precision and fraction reference table make it equally useful for rough carpentry estimates and precision machining tolerances.

How to Use the Inputs

1. Select conversion direction: Inches → Other Unit or Other Unit → Inches.
2. Choose your target unit from the dropdown (cm, mm, m, ft, yd, µm, or mi).
3. Enter the numeric value in the input field.
4. Adjust decimal places if you need more or less precision.
5. Use preset buttons for common values like 12 inches (1 ft) or 36 inches (1 yd).
6. Review all conversions in the output grid and the full all-units table.
7. Expand the inch fractions table for a machinist-ready fraction-to-metric reference.

Example Calculation

Tips & Best Practices

• The inch is defined as exactly 25.4 mm — this is an exact value, not an approximation.
• For quick mental math: 1 inch ≈ 2.5 cm. This gives a ballpark within 2% accuracy.
• Fractional inches (1/8, 1/16, 1/32) are common in US woodworking and machining — use the fractions table for quick metric equivalents.
• Screen resolution is measured in PPI (pixels per inch) — a 96 PPI display has pixels about 0.264 mm wide.
• When buying fasteners, M-series (metric) and inch-series bolt sizes do not overlap — always verify which system your project uses.
• The international inch (25.4 mm) replaced the slightly different US survey inch (deprecated in 2023).

The History of the Inch

The inch traces back to at least the 7th century, originally defined as the width of a man's thumb or three barleycorns laid end to end. Over centuries, different countries had slightly different inch lengths. The international agreement of 1959 standardized the inch at exactly 25.4 millimeters, finally resolving discrepancies between the US, UK, and Commonwealth nations.

Inches in Everyday Life

Screen sizes (TVs, phones, monitors) are measured diagonal in inches. Tire rim diameters use inches. Pipe sizes, bolt sizes, lumber dimensions (nominal vs. actual), and screw gauges in the US all rely on inches. Even in metric countries, screen sizes are conventionally quoted in inches.

Precision Considerations

For general purposes, two decimal places suffice (e.g., 2.54 cm per inch). Machining tolerances may require four or more decimals. CNC programs and engineering drawings often specify dimensions in thousandths of an inch ("thou" or "mil"), where 1 mil = 0.001 inch = 0.0254 mm.

Frequently Asked Questions

• How many centimeters are in an inch?

  Exactly 2.54 centimeters. This is an exact, defined value — the international inch has been precisely 25.4 mm since 1959.

• How do I convert inches to feet?

  Divide the number of inches by 12. For example, 66 inches ÷ 12 = 5.5 feet, which is 5 feet 6 inches.

• What is the difference between a US survey inch and an international inch?

  The US survey inch was 1/39.37 of a meter (≈25.4000508 mm), while the international inch is exactly 25.4 mm. The survey inch was officially deprecated by NIST in 2023.

• How do I read fractional inches?

  Fractional inches use powers of 2 as denominators: 1/2, 1/4, 1/8, 1/16, 1/32, and 1/64. Each step halves the previous division. For example, 3/8″ means three of the eight equal parts of an inch.

• Why are inches still used instead of metric?

  The US, Liberia, and Myanmar have not fully adopted the metric system. In the US, inches are deeply embedded in construction, manufacturing standards, and everyday life. Many industries use both systems in parallel.

• How many inches are in a mile?

  There are 63,360 inches in a mile. One mile = 5,280 feet × 12 inches/foot = 63,360 inches.