1 MCM = 1 kcmil = 1,000 circular mils ≈ 0.506707479 mm². Convert conductor area in either direction below. For example, 250 MCM = 126.676870 mm² and 500 MCM = 253.353740 mm².
MCM / kcmil to mm² calculator
Use a decimal point or comma: 250.5 or 250,5. Write thousands without separators: 1000. Choosing a preset switches to MCM → mm².
250 × 0.5067074791 ≈ 126.676870 mm²
Area conversion only; the result does not determine cable ampacity or interchangeability.
MCM to mm² conversion table
MCM and kcmil have the same numerical value. The areas below are mathematical conversions, rounded to six decimal places; they are not a list of interchangeable cable products. The CSV uses the same calculation.
| MCM / kcmil | Area (mm²) | Circular mils |
|---|---|---|
| 250 | 126.676870 | 250,000 |
| 300 | 152.012244 | 300,000 |
| 350 | 177.347618 | 350,000 |
| 400 | 202.682992 | 400,000 |
| 450 | 228.018366 | 450,000 |
| 500 | 253.353740 | 500,000 |
| 550 | 278.689114 | 550,000 |
| 600 | 304.024487 | 600,000 |
| 650 | 329.359861 | 650,000 |
| 700 | 354.695235 | 700,000 |
| 750 | 380.030609 | 750,000 |
| 800 | 405.365983 | 800,000 |
| 900 | 456.036731 | 900,000 |
| 1000 | 506.707479 | 1,000,000 |
| 1250 | 633.384349 | 1,250,000 |
| 1500 | 760.061219 | 1,500,000 |
| 1750 | 886.738088 | 1,750,000 |
| 2000 | 1013.414958 | 2,000,000 |
How to convert MCM, circular mils and mm²
A circular mil is the area of a circle with a diameter of one mil, or 0.001 inch. Since one mil is 0.0254 mm, its area is π × (0.0254 mm)² ÷ 4. Multiplying by 1,000 gives the area represented by one kcmil.
- mm² = MCM × π × 0.0254² × 1,000 ÷ 4, approximately MCM × 0.5067074791.
- MCM = mm² ÷ 0.5067074791, approximately mm² × 1.9735252414.
- Circular mils = MCM × 1,000.
- mm² = circular mils × 0.0005067074791.
The calculator uses the geometric expression with π rather than a shortened decimal factor. NIST lists the circular-mil conversion in SP 811, Appendix B.9, area conversion factors.
Avoid the factor-of-1,000 error: 1,000,000 circular mils equals 1,000 MCM, approximately 506.707479 mm². It does not equal 1 MCM. A circular mil is also different from a square mil: a square mil is the area of a square with sides one mil long.
Six worked conversion examples
250 MCM to mm²
250 × 0.5067074791 ≈ 126.676870 mm². The same conductor area may be written 250 kcmil or 250,000 circular mils.
350 MCM to mm²
350 × 0.5067074791 ≈ 177.347618 mm². The same conductor area may be written 350 kcmil or 350,000 circular mils.
500 MCM to mm²
500 × 0.5067074791 ≈ 253.353740 mm². The same conductor area may be written 500 kcmil or 500,000 circular mils.
750 MCM to mm²
750 × 0.5067074791 ≈ 380.030609 mm². The same conductor area may be written 750 kcmil or 750,000 circular mils.
240 mm² to MCM
240 ÷ 0.5067074791 ≈ 473.646058 MCM. Keep this calculated area separate from the nominal size printed in a cable catalog.
300 mm² to MCM
300 ÷ 0.5067074791 ≈ 592.057572 MCM. Keep this calculated area separate from the nominal size printed in a cable catalog.
Does a converted area identify a replacement cable?
No. An area conversion describes geometry. It does not establish ampacity, conductor resistance, temperature rating, voltage rating, installation suitability or terminal compatibility. Copper and aluminum use the same area conversion factor; their electrical and thermal behavior differs.
For example, 500 MCM is 253.353740 mm², so it is not exactly 240 mm², 250 mm² or 300 mm². Replacing it with a nearby catalog size requires a separate design check. Choosing a larger numerical area alone does not establish compliance.
- Identify the original conductor material, construction, insulation, rating and installation conditions.
- Compare the candidate cable’s manufacturer data, including conductor resistance and applicable current ratings.
- Check load current, temperature, grouping, terminals, voltage drop and short-circuit requirements for the installation.
For the next steps, use our wire ampacity calculator and AWG/kcmil voltage drop calculator, within their stated assumptions.
Frequently asked questions
Are MCM and kcmil the same?
Yes. Both denote one thousand circular mils. A conductor labeled 350 MCM has the same nominal area designation as 350 kcmil.
Is 250 MCM the same as 250 mm²?
No. 250 MCM is approximately 126.676870 mm². Conversely, 250 mm² is approximately 493.381310 MCM.
Is the diameter shown the cable outside diameter?
No. It is the diameter of a solid circle having the calculated area. Stranding, compaction and insulation change a cable’s actual dimensions. Use the manufacturer’s outside diameter for conduit fill or termination fit.
Does aluminum use a different conversion factor?
No. MCM to mm² is a unit conversion independent of material. Equal areas of copper and aluminum do not necessarily have equal resistance or current capacity.
Can I convert AWG using this MCM factor?
AWG is a gauge scale, so its number is not multiplied directly by 0.5067074791. Use the mm² to AWG converter to compare AWG areas and diameters.
Why do tables show 506.7 for 1000 MCM?
That is the rounded area in mm²: 1000 × 0.5067074791 ≈ 506.7. Keep the input unit and the number together to avoid mistaking this for the factor for one MCM.
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