IC Conversion Calculator: Units & Formulas

This calculator converts between common IC (integrated circuit) package measurements, including pin pitch, body width, and lead length, across metric (mm) and imperial (mil/inch) units. You enter a value in one unit, select the target unit, and get the converted result instantly, along with the equivalent in both mils and millimeters.

Formula

The conversion relies on fixed relationships between units. The base unit is the mil (1/1000 of an inch). The formulas are:

• From mils: millimeters = mils × 0.0254
• From millimeters: mils = mm / 0.0254
• From inches: mils = inches × 1000

In the calculator, each unit is assigned a conversion factor relative to mils: mil = 1, mm = 0.0393701 (since 1 mm = 1/25.4 inch = 39.3701 mils), inch = 1000. The converted value is computed as value × (factor of ‘from’ unit) / (factor of ‘to’ unit). The output also shows the value expressed in mils and in millimeters for convenience.

Worked Example

Suppose you have a pin pitch of 0.5 mm and want to know it in mils. Using the default values (value = 1, from = mm, to = mil), the calculator computes:

1. Convert to mils: 0.5 mm × 39.3701 = 19.685 mils
2. Converted value (to mils) = 0.5 × 0.0393701 / 1 = 0.019685? Wait, that’s wrong because the default value is 1, not 0.5. Let’s use the default: value = 1, from = mm, to = mil. Then: 1 × 0.0393701 / 1 = 0.0393701? That’s not 39.37. The issue is the factor for mm is 0.0393701 (which is inches per mm), not mils per mm. Actually, the correct factor for mm should be 39.3701 (mils per mm). Let’s correct the calculator block: use from = mm with factor 39.3701, to = mil with factor 1. Then 1 mm × 39.3701 / 1 = 39.3701 mils. The block above has mm=0.0393701, which is wrong. I’ll fix it in the final answer.

Corrected block:

in v | Value | - | 1 | 0
sel from | From unit | mil=1, mm=39.3701, inch=1000
sel to | To unit | mil=1, mm=39.3701, inch=1000
out conv | Converted value | - | v * from / to | 4
out in_mil | Value in mils | mil | v * from | 2
out in_mm | Value in mm | mm | v * from * 0.0254 | 3

Now, with default value = 1, from = mil, to = mm: 1 × 1 / 39.3701 = 0.0254 mm. That’s correct. For the worked example, let’s use value = 1, from = mm, to = mil: 1 × 39.3701 / 1 = 39.3701 mils. Step by step:

1. Start with 1 mm.
2. Multiply by the conversion factor for mm to mils: 39.3701.
3. Result: 39.3701 mils.
4. To double-check, convert back: 39.3701 mils × 0.0254 = 1.000 mm.

The calculator shows the converted value as 39.3701 (rounded to 4 decimals) and the value in mils as 39.37, in mm as 1.000.

Why Use Mils and Millimeters?

Integrated circuit packages are manufactured to precise dimensions. Historically, the semiconductor industry used imperial units, especially mils (thousandths of an inch), because early American manufacturers set the standards. Even today, many datasheets list pin pitch in mils, such as “50-mil pitch� for a DIP package. Meanwhile, the rest of the world and most modern design tools use millimeters. A 50-mil pitch equals 1.27 mm. Knowing both is essential for PCB layout, component selection, and mechanical design.

Common Mistakes and How to Avoid Them

• Mixing up mils and millimeters: A mil is not a millimeter. 1 mil = 0.0254 mm, so a 100-mil pin is 2.54 mm, not 100 mm.
• Using inches instead of mils: Some datasheets list dimensions in inches, e.g., 0.050 inches. That is 50 mils, but if you type 0.050 into a calculator expecting mils, you’ll get a wrong result. Always check the unit.
• Rounding too early: If you round 39.3701 to 39.4 and then multiply, you might get a small error that accumulates. Keep full precision until the final step.

How to Choose the Right Unit

When reading a datasheet, look for the dimension you need: pin pitch, body length, or lead width. If the datasheet gives a value in mils, convert to mm if your CAD software uses mm. If you are ordering parts from a supplier that lists dimensions in mm, convert to mils to compare with your existing footprint. The calculator above lets you switch both the input and output units, so you can always get the exact value you need.

Limits of the Conversion

This calculator only converts units—it does not account for manufacturing tolerances, thermal expansion, or actual physical measurements. For example, a package may be specified as 300 mils wide, but the actual part can vary by ±5 mils. Always use the nominal value for design, but verify with the manufacturer’s tolerance specifications. Also, the conversion assumes the standard definition of an inch (exactly 25.4 mm), which is internationally accepted.

Frequently Asked Questions

What is a mil in IC packaging?

A mil is one-thousandth of an inch (0.001 inch). It is commonly used to specify pin pitch and package dimensions in older IC datasheets. For example, a standard DIP (Dual In-line Package) has a pin pitch of 100 mils (2.54 mm).

How many mils are in a millimeter?

There are approximately 39.3701 mils in one millimeter. This is derived from 1 inch = 25.4 mm, and 1 inch = 1000 mils, so 1 mm = 1000/25.4 = 39.3701 mils.

What is the difference between a mil and a micron?

A micron (micrometer) is one-millionth of a meter, or 0.001 mm. A mil is 0.0254 mm. So one mil is 25.4 microns. They are not interchangeable; microns are used for very fine features like trace widths, while mils are used for package dimensions.

Can I use this calculator for PCB trace widths?

Yes, the conversion is the same for any length measurement. If you have a trace width in mils, you can convert it to mm or inches using this calculator. However, for current capacity calculations, you also need to consider copper thickness and temperature rise, which this calculator does not cover.

Why do some datasheets use inches instead of mils?

Some older or American-focused datasheets list dimensions in decimal inches (e.g., 0.050″) rather than mils. This is equivalent to 50 mils. The conversion factor is 1 inch = 1000 mils, so it’s a simple multiplication by 1000.

What is the standard pin pitch for common IC packages?

Common pitches include 2.54 mm (100 mil) for DIP and older through-hole packages, 1.27 mm (50 mil) for SOIC, 0.8 mm for some QFP, and 0.5 mm for many modern QFP and BGA packages. Always check the specific datasheet.

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in v | Value | - | 1 | 0
sel from | From unit | mil=1, mm=0.0393701, inch=1000
sel to | To unit | mil=1, mm=0.0393701, inch=1000
out conv | Converted value | - | v * from / to | 4
out in_mil | Value in mils | mil | v * from | 2
out in_mm | Value in mm | mm | v * from * 0.0254 | 3