Convert Square Mil to Square Inch
Convert square mils to square inches instantly. 1 square mil = 1e-6 square inch — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Square Inch to Square Mil converter for the reverse conversion.
Units explained
Square Mil
A square mil is an imperial unit of area equal to 6.4516×10⁻¹⁰ m². It is widely used in printed circuit board (PCB) design and electronics manufacturing.
Derived by squaring the mil (1 mil = 1/1000 of an inch = 0.0254 mm). Standardized via the 1959 International Yard and Pound Agreement.
Square mils are the standard unit for PCB trace cross-sections, pad areas, and component pitches in US-localized electronic design software and datasheets.
Standardized via the 1959 International Yard and Pound Agreement.
Square Inch
A square inch is an imperial unit of area equal to exactly 0.00064516 m², the area of a square with sides of one inch. It is widely used in the United States for small-area measurements.
Derived by squaring the inch. The inch was standardized to exactly 25.4 mm via the 1959 International Yard and Pound Agreement.
Square inches are used extensively in US engineering, manufacturing, real estate (for floor plans), and everyday small-area measurements. Engine displacement is often expressed in cubic inches but cross-sections in square inches.
Inch dates to medieval English usage; modern exact value standardized in 1959.
Square Mil to Square Inch conversion formula
The relationship between square mils and square inches:
To convert square mils to square inches, multiply the value in square mils by 1e-6. To reverse, multiply square inches by 1000000.
How to use this converter
Type a value into the calculator. The result in square inches updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Square Inch to Square Mil converter for the reverse direction.
Step-by-step: convert square mils to square inches
- Write down the value in square mils (mil²).
- Multiply that value by the factor 1e-6.
- The product is the equivalent value in square inches (in²).
- To reverse, multiply the square inch value by 1000000.
Worked examples
Example 1 — Convert 1 mil² to in²:
1 × 1e-6 = 1e-6 in²
Example 2 — Convert 100 mil² to in²:
100 × 1e-6 = 1e-4 in²
Real-world example — Sub-visible-light wavelength
500 square mils (the green-yellow visible band) equals 0.5 square inches — the canonical conversion in optics between wavelength specifications and micron-scale lens-coating thicknesses.
500 mil² × 1e-6 = 0.0005 in²
Real-world example — Spanning sub-micron to micron scale
Crossing from square mils to square inches is the everyday workflow of microscopy and semiconductor engineering — a measurement of 1000 square mils translates to a much more compact value in square inches that fits the scale of biological cells and process nodes.
1000 mil² × 1e-6 = 0.001 in²
Square Mil to Square Inch conversion table
Standard reference values for converting square mils to square inches:
| Square Mil [mil²] | Square Inch [in²] |
|---|---|
| 0.01 | 1e-8 |
| 0.1 | 1e-7 |
| 1 | 1e-6 |
| 2 | 2e-6 |
| 3 | 3e-6 |
| 4 | 4e-6 |
| 5 | 5e-6 |
| 10 | 1e-5 |
| 20 | 2e-5 |
| 30 | 3e-5 |
| 40 | 4e-5 |
| 50 | 5e-5 |
| 100 | 1e-4 |
| 500 | 0.0005 |
| 1000 | 0.001 |
Frequently asked questions
How many square inches is 1 square mil?
How do I convert square mils to square inches?
How do I convert square inches back to square mils?
How many square inches is 100 square mils?
Popular area unit conversions
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Metric / SI (5 units)
Imperial / US Customary (14 units)
Sources & references
Conversion factor (1 mil² = 1e-6 in²) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- NIST — Refinement of values for the yard and pound (Federal Register 1959)
The treaty (signed by US
- International Astronomical Union — System of Astronomical Constants
The IAU defines astronomical units including the AU (149597870700 m exactly) light-year and parsec used in astronomy and astrophysics.