About

Electrical engineers and contractors frequently need to verify the remaining length of wire on a partially used spool without unrolling it. This tool calculates linear length based on the net weight of the conductor and its cross-sectional area defined by the American Wire Gauge (AWG) system.

The calculation is sensitive to the material density (Copper vs. Aluminum) and the presence of insulation. Since insulation adds weight without adding conductivity, an approximation factor is applied for insulated wires to prevent overestimation of the conductive length. This is essential for inventory checks and planning raceway pulls.

Formulas

Length L is calculated from Mass m, Density ρ, and Area A.

L = mρ × A × InsulationFactor

Standard Densities: Copper ρ ≈ 8960 kg/m³, Aluminum ρ ≈ 2700 kg/m³.

Reference Data

AWG	Diameter (mm)	Area (mm²)	Copper Mass (kg/km)
10	2.588	5.26	47.14
12	2.053	3.31	29.65
14	1.628	2.08	18.66
16	1.291	1.31	11.73
18	1.024	0.823	7.37
20	0.812	0.518	4.64
24	0.511	0.205	1.83
30	0.255	0.051	0.46

Frequently Asked Questions

Insulation thickness varies by manufacturer and type (THHN, XHHW, PVC). This tool adds a conservative 15-20% weight buffer for insulation when selected. For exact results, weigh a 1-meter sample to determine the specific linear density.

The AWG standard relies on the total cross-sectional area of the conductor. While stranded wire has air gaps increasing diameter, the weight-to-copper-volume ratio remains roughly consistent with solid core wire of the same gauge.

Copper is significantly denser (8.96 g/cm³) than Aluminum (2.70 g/cm³). A 1 kg spool of Aluminum wire will be more than 3 times longer than a 1 kg spool of Copper wire of the same gauge.

Spools (plastic or wood) have significant weight. You must subtract the weight of the empty spool from the total weight to get the Net Weight of the wire, otherwise, the length calculation will be grossly exaggerated.