Convert Square Thou to Square Millimeter
Convert square thous to square millimeters instantly. 1 square thou = 0.00064516 square millimeter — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Square Millimeter to Square Thou converter for the reverse conversion.
Units explained
Square Thou
A square thou is an imperial unit of area equal to 6.4516×10⁻¹⁰ m², identical to the square mil. The word 'thou' is short for 'thousandth' (of an inch).
Identical in value to the square mil; 'thou' is the British engineering term, 'mil' is the American term. Both refer to 1/1000 of an inch.
Square thous are used in British and Commonwealth engineering contexts where 'thou' is preferred over 'mil', particularly in mechanical engineering tolerance specifications.
Standardized via the 1959 International Yard and Pound Agreement.
Square Millimeter
A square millimeter is a metric unit of area equal to 10⁻⁶ m² (1 mm × 1 mm). It is widely used in engineering, electronics, and small-scale technical work.
Derived by squaring the millimeter, defined as 1/1000 of a meter. The milli- prefix comes from the Latin 'mille' (thousand).
Square millimeters express PCB trace cross-sections, the area of small mechanical features in CAD drawings, biological sample sizes, and material thicknesses.
Millimeter has been part of the metric system since 1795.
Square Thou to Square Millimeter conversion formula
The relationship between square thous and square millimeters:
To convert square thous to square millimeters, multiply the value in square thous by 0.00064516. To reverse, multiply square millimeters by 1550.0031000062.
How to use this converter
Type a value into the calculator. The result in square millimeters 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 Millimeter to Square Thou converter for the reverse direction.
Step-by-step: convert square thous to square millimeters
- Write down the value in square thous (thou²).
- Multiply that value by the factor 0.00064516.
- The product is the equivalent value in square millimeters (mm²).
- To reverse, multiply the square millimeter value by 1550.0031000062.
Worked examples
Example 1 — Convert 1 thou² to mm²:
1 × 0.00064516 = 0.00064516 mm²
Example 2 — Convert 100 thou² to mm²:
100 × 0.00064516 = 0.064516 mm²
Real-world example — Spanning sub-micron to micron scale
Crossing from square thous to square millimeters is the everyday workflow of microscopy and semiconductor engineering — a measurement of 1000 square thous translates to a much more compact value in square millimeters that fits the scale of biological cells and process nodes.
1000 thou² × 0.00064516 = 0.64516 mm²
Real-world example — Sub-visible-light wavelength
500 square thous (the green-yellow visible band) equals 0.5 square millimeters — the canonical conversion in optics between wavelength specifications and micron-scale lens-coating thicknesses.
500 thou² × 0.00064516 = 0.32258 mm²
Square Thou to Square Millimeter conversion table
Standard reference values for converting square thous to square millimeters:
| Square Thou [thou²] | Square Millimeter [mm²] |
|---|---|
| 0.01 | 6.4516e-6 |
| 0.1 | 6.4516e-5 |
| 1 | 0.00064516 |
| 2 | 0.00129032 |
| 3 | 0.00193548 |
| 4 | 0.00258064 |
| 5 | 0.0032258 |
| 10 | 0.0064516 |
| 20 | 0.0129032 |
| 30 | 0.0193548 |
| 40 | 0.0258064 |
| 50 | 0.032258 |
| 100 | 0.064516 |
| 500 | 0.32258 |
| 1000 | 0.64516 |
Frequently asked questions
How many square millimeters is 1 square thou?
How do I convert square thous to square millimeters?
How do I convert square millimeters back to square thous?
How many square millimeters is 100 square thous?
Popular area unit conversions
Convert Square Thou to other area units
Show all Square Thou conversions
Metric / SI (5 units)
Imperial / US Customary (14 units)
Sources & references
Conversion factor (1 thou² = 0.00064516 mm²) 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 Hydrographic Organization — Resolution on the Nautical Mile
International authority that standardised the nautical mile at exactly 1852 m in 1929 — the value adopted worldwide for sea and air navigation.