Find the right cable cross-section for your load current and run length, with an estimated voltage drop check and a matching MCCB rating.
Enter your load, supply, and cable run details to get a recommended cable size.
Enter your details and hit calculate
Calculate to compare current rating and voltage drop across nearby cable sizes.
Choosing the correct cable size is one of the most fundamental — and most frequently rushed — steps in any electrical installation. Undersize a cable and it can overheat, degrade its insulation, and become a fire risk. Oversize it by too much and you pay for copper or aluminium you don't need. This calculator estimates the right cable cross-sectional area for a given electrical load by first finding the full-load current from voltage, power, and power factor, then matching that current against a standard current-carrying-capacity table for copper or aluminium conductors. It also applies a length-based derating step, since longer cable runs suffer greater voltage drop and resistive losses, often requiring the next size up even when the base current rating would technically suffice.
The current is derived from the same single-phase and three-phase relationships used throughout electrical sizing: for single-phase, I = (kW × 1000) ÷ (V × PF), and for three-phase, I = (kW × 1000) ÷ (√3 × V × PF). Once current is known, it's checked against a cable size table (sized differently for copper vs aluminium, since aluminium has lower conductivity and needs a larger cross-section for the same current). For runs longer than 30 m, the calculator bumps the cable size up a step or more to compensate for voltage drop over distance, and a matching MCCB rating is suggested based on the same calculated current.
Voltage drop estimate. Beyond the standard size-and-length step-up rule, this calculator also computes an approximate voltage drop percentage at the recommended cable size, using the conductor's typical resistance per kilometre. For single-phase runs, Vd = (2 × I × L × R) ÷ 1000, and for three-phase runs, Vd = (√3 × I × L × R) ÷ 1000, where R is the conductor resistance in ohms/km, L is the one-way cable length in metres, and I is the full-load current. The result is expressed as a percentage of supply voltage and flagged against the commonly used 3% voltage-drop guideline for final sub-circuits — a quick sanity check on top of the table-based size recommendation, so you can see whether the recommended size is comfortably within limits or borderline.
The comparison table below the result shows current rating and estimated voltage drop side by side for the recommended size and its immediate neighbours, so you can see at a glance whether stepping up (or down) a size meaningfully changes the voltage drop for your specific run length.
This tool is especially useful for electrical contractors and engineers planning a new circuit, panel feeder, or distribution run who need a starting-point cable size, voltage drop indication, and breaker rating before consulting a full derating and voltage-drop table for the final installation design.
Every conductor has resistance, and current flowing through that resistance generates heat (I²R losses). If a cable is too thin for the current it carries, it heats up beyond the safe rating of its insulation, which accelerates insulation ageing and, in the worst case, leads to a fire. This is why every conductor size has a published current-carrying capacity (also called ampacity) for a given installation method, insulation type, and ambient temperature. At the same time, resistance also causes a voltage drop along the cable's length: the further the load is from the source, the more voltage is "lost" in the wire before it reaches the equipment. A motor or panel that receives a significantly lower voltage than it was designed for can overheat, underperform, or trip on undervoltage — which is why voltage drop, not just current rating, has to be checked separately for long cable runs.
In India, low-voltage power and control cables are commonly manufactured and rated to IS 7098 (PVC insulated cables) and related IS/IEC standards, while installation practices for derating and voltage drop typically follow IEC 60364 principles. These standards publish current-carrying capacity tables for different conductor sizes, insulation types, and installation methods (free air, tray, conduit, buried), along with correction factors for ambient temperature, grouping of multiple circuits, and soil resistivity for buried cables. The current-carrying capacity values and conductor resistance figures used in this calculator are representative, single-core, PVC-insulated, free-air/tray reference values commonly seen in such tables — useful for quick, preliminary sizing, but not a substitute for the full derated table specific to your exact installation condition.
Getting an accurate recommendation only takes four inputs:
| Size (sq.mm) | Copper Rating |
|---|---|
| 1.5 | 10 A |
| 2.5 | 16 A |
| 4 | 25 A |
| 6 | 32 A |
| 10 | 40 A |
| 16 | 63 A |
| 25 | 80 A |
Larger sizes (120–400 sq.mm) are also supported by the calculator above but omitted here for brevity — enter your full-load current above to see the full recommendation including MCCB rating and voltage drop.
Example: Three-phase load of 20 kW at 415 V, PF = 0.85, cable run = 60 m, copper conductor. Current = (20 × 1000) ÷ (1.732 × 415 × 0.85) ≈ 32.7 A. Base cable size = 10 sq.mm (40 A rating). Since the run exceeds 50 m, the recommended size steps up to compensate for voltage drop, and the calculator's voltage-drop estimate confirms whether the stepped-up size keeps the drop comfortably under the typical 3% guideline, alongside a matching MCCB suggestion.
Reference: Current-carrying capacity and standard resistance values are approximate figures commonly used in electrical engineering handbooks and IS 7098 / IEC 60364-based sizing tables. This calculator is for preliminary, educational planning only and does not replace a full derating and voltage-drop calculation to the applicable local wiring code.
Content last reviewed: July 2026 · Reference standards: IS 7098, IEC 60364
Longer cable runs have more resistance, which causes a larger voltage drop for the same current. Even if a smaller cable can technically carry the current safely, a long run may cause the voltage at the load end to drop too much, so this calculator steps up the recommended size for longer runs and shows an estimated voltage drop percentage to back that up.
It's an approximate percentage of your supply voltage that is "lost" to cable resistance over the given run length, calculated using a typical resistance-per-km value for the chosen conductor and size. Many wiring codes recommend keeping this under roughly 3% for a final sub-circuit. It's a useful sanity check, but actual drop can vary with cable construction, temperature, and installation method.
Aluminium has lower electrical conductivity than copper — roughly 61% as conductive for the same cross-section. To carry the same current with an acceptable temperature rise and voltage drop, an aluminium conductor needs a larger cross-sectional area than an equivalent copper conductor, which is why the two materials use separate sizing tables here.
The calculator picks the next standard MCCB frame size at or above your calculated full-load current, from a list of commonly available ratings. This is a starting point only — actual breaker selection should also account for cable current-carrying capacity, discrimination with upstream/downstream protection, and any short-circuit or coordination study required for the installation.
No — this is a preliminary, educational estimate using standard formulas and typical resistance values. A final installation design should also account for ambient temperature derating, grouping of multiple cables, installation method (conduit, tray, buried, etc.), harmonic loading, and the specific requirements of your local electrical code, ideally reviewed by a qualified electrical engineer.
As a rough guide under IS 7098-based free-air ratings, a 4 sq.mm copper cable is typically good for around 25 A, 6 sq.mm for around 32 A, and 10 sq.mm for around 40 A. The exact figure depends on insulation type, installation method, ambient temperature, and grouping with other cables, which is why this calculator also applies a length-based voltage drop check rather than relying on current rating alone. See the reference chart above for the full range of sizes.
Yes, for a quick estimate. Select single phase, enter your supply voltage (typically 230 V), your connected load in kW, and the wire run length from the distribution board to the point of use. For most domestic circuits, keeping the estimated voltage drop under 3% and choosing the next standard cable size above the calculated minimum is a safe, conservative approach — but always have the final wiring plan checked against your local wiring code.