Calculate cable diameter, strand diameter, or number of strands from any two values with mm, cm, m, in, or ft units and show steps.
Customize This Calculator
Build your own version. Describe what you want changed, added, or compared.
Related Calculators
- Lashing Capacity Calculator
- Snub Force Calculator
- Percent Elongation Calculator
- Hoist Motor Power Calculator
- All Construction Calculators
Cable Strand Size Formula
The cable strand size calculator uses an idealized relationship between total cable diameter, strand diameter, and number of strands. Enter any two values to solve for the missing value.
- D = cable diameter
- d = individual strand diameter
- N = number of strands
- N = number of strands
- D = cable diameter
- d = individual strand diameter
- d = individual strand diameter
- D = cable diameter
- N = number of strands
The calculator converts length inputs to millimeters internally, applies the formula, then converts the result back to the unit selected for the missing field.
- Calculate cable diameter: use strand diameter and number of strands.
- Calculate number of strands: use cable diameter and strand diameter.
- Calculate strand diameter: use cable diameter and number of strands.
Common Cable and Strand Diameter Units
Use the same physical measurement units when checking calculations by hand. The calculator can accept mixed units because it converts them before solving.
| Unit | Equivalent in millimeters | Typical use |
|---|---|---|
| 1 mm | 1 mm | Small strand and cable measurements |
| 1 cm | 10 mm | Larger cable diameters |
| 1 in | 25.4 mm | Imperial cable sizing |
| 1 ft | 304.8 mm | Very large length references, rarely used for strand diameter |
Typical Strand Counts and Diameter Multipliers
The multiplier shows how many times larger the calculated cable diameter is than one strand diameter using this formula.
| Number of strands | Diameter multiplier, āN | If strand diameter is 1 mm |
|---|---|---|
| 7 | 2.646 | 2.646 mm cable diameter |
| 19 | 4.359 | 4.359 mm cable diameter |
| 37 | 6.083 | 6.083 mm cable diameter |
| 61 | 7.810 | 7.810 mm cable diameter |
Example Cable Strand Size Calculations
Example 1: Calculate cable diameter
You have 19 strands, and each strand has a diameter of 0.5 mm.
The calculated cable diameter is 2.1794 mm.
Example 2: Calculate strand diameter
You have a cable diameter of 10 mm and 25 strands.
The calculated strand diameter is 2 mm.
FAQ
Why does the calculator use the square root of the number of strands?
The formula treats the cable size as scaling with the square root of the strand count. This comes from comparing circular cross-sectional areas in a simplified way. If you increase the number of equal strands, the total area increases in proportion to the strand count, while the equivalent diameter increases with the square root of that count.
Can the number of strands be a decimal?
The formula can return a decimal when calculating the number of strands, but a real cable must have a whole number of strands. If the result is not a whole number, round to a practical strand count and then recalculate the resulting cable or strand diameter.
Is this the same as an exact cable outside diameter?
No. This is an idealized size calculation based on strand count and strand diameter. Actual outside diameter can differ because of strand lay, packing arrangement, insulation, jacket thickness, coatings, and manufacturing tolerances.