What this converter does
This converter changes a second moment of area — the section’s moment of inertia — from mm⁴ to in⁴ and back. It also covers cm⁴ (metric steel tables) and m⁴. Type a value, pick your units, and read the result instantly.
The factor is exactly 25.4⁴ = 416,231 mm⁴ per in⁴, since an inch is exactly 25.4 mm. So results are precise, not rounded.
The units it covers
Second moment of area has units of length⁴, so each unit converts through mm⁴ by a fixed factor.
View all units & their values
| Unit | Symbol | Value | Mainly used |
|---|---|---|---|
| Millimetre⁴ | mm⁴ | 1 | Metric section data |
| Centimetre⁴ | cm⁴ | 10,000 | Steel section tables (Ix) |
| Inch⁴ | in⁴ | 416,231 | US steel section tables |
| Metre⁴ | m⁴ | 1e12 | Large sections, analysis |
The formula
Each length⁴ unit has a fixed value in mm⁴, so the conversion is one multiplication:
result = value × factor_from ÷ factor_toWhere:
- value = the second moment you typed
- factor_from = its value in mm⁴
- factor_to = the target unit’s value in mm⁴
Worked example
Convert 5,000 cm⁴ (a steel beam Ix) to in⁴.
5,000 cm⁴ × 10,000 = 5.0e7 mm⁴5.0e7 ÷ 416,231 = 120.1 in⁴So 5,000 cm⁴ ≈ 120 in⁴ — a typical mid-size steel beam.
The units in this example
The SI-based unit for second moment of area. Metric section tables often list it as cm⁴ (1 cm⁴ = 10,000 mm⁴).
- 1 in⁴ = 416,231 mm⁴
- 1 cm⁴ = 10,000 mm⁴
- 1 m⁴ = 1e12 mm⁴
- 1 mm⁴ ≈ 2.4e-6 in⁴
The US customary unit for moment of inertia, listed in AISC steel section tables.
- 1 in⁴ = 416,231 mm⁴
- 1 in⁴ = 41.62 cm⁴
- 100 in⁴ ≈ 4,162 cm⁴
- factor = 25.4⁴