Wire Size Calculator
Estimate electrical conductor size from current, voltage-drop limit, cable length, material and operating temperature, with metric mm² and AWG/kcmil recommendations.
Electrical wire sizing workspace
Enter the system, current, one-way cable distance and allowable voltage drop. The calculator sizes each conductor by voltage-drop physics.
How the Wire Size Calculator Works
This calculator estimates the minimum conductor cross-sectional area needed to keep a selected voltage drop below your limit. It combines Ohm's law with conductor resistance. For DC and single-phase circuits, the current travels to the load and back, so the resistive path uses twice the one-way cable length. For balanced three-phase AC, the voltage-drop relationship uses a √3 factor instead.
The core equation is A = k × I × ρ(T) × L ÷ ΔV, where A is conductor area, I is current, L is one-way distance, ΔV is allowable voltage drop, ρ(T) is temperature-adjusted resistivity, and k is 2 for DC/single-phase or √3 for three-phase. The result is converted to mm², then rounded upward to common metric and AWG/kcmil conductor sizes.
The calculator uses typical 20 °C conductor properties for annealed copper and Aluminum 1350, then adjusts resistivity with temperature. Actual cable construction, alloy, stranding and manufacturer data can vary, so the result should be treated as a design estimate rather than a substitute for cable data sheets.
How to Use the Electrical Wire Size Calculator
- Choose DC / AC single-phase or AC three-phase.
- Enter source voltage and set the allowable voltage drop as either a percentage or volts.
- Select copper or aluminum and enter the maximum load current.
- Enter the one-way cable run in meters, feet or kilometers.
- Enter the estimated conductor operating temperature and number of parallel conductors per path or phase.
- Select Calculate to see the required area, recommended standard sizes and voltage-drop details.
Worked Example: 230 V Copper Circuit
For a 230 V single-phase circuit, 20 A load, 20 m one-way run, 3% voltage-drop limit, annealed copper and an estimated conductor temperature of 60 °C, the voltage-drop calculation requires about 2.31 mm². The next common metric size is 2.5 mm². The nearest rounded AWG recommendation is shown separately because AWG sizes do not line up exactly with metric conductor sizes.
12 V, 24 V, 48 V and Low-Voltage Wiring
Low-voltage DC systems are especially sensitive to cable length. A 0.6 V drop is only about 0.26% of a 230 V supply but 5% of a 12 V supply. That is why batteries, solar systems, LED lighting, pumps, automotive accessories and other 12 V or 24 V loads may need surprisingly large conductors over long runs. Enter the actual source voltage and a realistic voltage-drop limit rather than assuming that a cable suitable for mains voltage is suitable for low-voltage DC.
Metric mm², AWG and kcmil
Many countries specify conductor size in square millimeters, while the United States commonly uses American Wire Gauge (AWG). Larger North American conductors are often stated in kcmil. This calculator shows both systems. Because standard sizes are discrete, the displayed metric size and AWG size are each independently rounded upward from the calculated cross-sectional area and therefore may not be exact equivalents.
For AWG, a smaller gauge number means a larger conductor. Sizes above 1/0 are written 2/0, 3/0 and 4/0; larger conductors are commonly expressed in kcmil.
Temperature and Conductor Material
Electrical resistivity increases as copper or aluminum gets hotter. The calculator adjusts the 20 °C reference resistivity using ρ(T) = ρ20 × [1 + α(T − 20)]. Aluminum has higher resistivity than copper, so an aluminum conductor generally needs more cross-sectional area to achieve the same resistive voltage drop. The temperature setting here changes resistance only; it is not an ampacity temperature-derating calculation.
Important Electrical Safety Limitations
Do not select a real installation conductor from voltage drop alone. A final cable must also satisfy the applicable electrical code and project requirements for ampacity, continuous-load rules, overcurrent protection, conductor insulation, ambient temperature, grouped/bundled conductors, conduit or raceway fill, terminal ratings, fault current, short-circuit withstand, grounding/earthing and installation method.
For long AC feeders, large cables, motors and loads with significant power factor or reactance, a resistance-only voltage-drop model can differ from a full AC impedance calculation. Use current local standards and a qualified electrician or electrical engineer for installation decisions.
Frequently Asked Questions
What is a normal voltage-drop percentage?
There is no single universal value for every installation. Project specifications and electrical codes vary. Enter the limit required for your circuit rather than treating a default value as a code rule.
Is cable distance one-way or round-trip?
Enter the one-way distance from source to load. The calculator automatically uses the return-path factor for DC and single-phase circuits.
Why is the recommended wire larger than the calculated area?
Manufactured conductor sizes are discrete. The calculator rounds upward to the next common standard size so the selected standard conductor is not smaller than the voltage-drop area calculated.
Can I calculate aluminum wire size?
Yes. Select Aluminum 1350. The tool uses a higher reference resistivity than copper and applies temperature correction.
Does this calculator determine breaker size?
No. Breaker/fuse selection and conductor ampacity require code-specific rules not represented by this voltage-drop calculation.
Does it work for three-phase?
Yes, for a balanced resistive voltage-drop approximation using line voltage and line current. More detailed AC systems may need impedance, reactance and power-factor analysis.