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Enter the load, the supply and the run length. You get the smallest copper size that carries the current, keeps volt drop inside 2.5%, and takes a standard breaker — with the numbers behind it. Sized for Pakistan supply: 230 V single-phase, 400 V three-phase.
Enter a load. The size, the capacity it needs where you are installing it, the volt drop over your run, and the breaker it takes all appear here.
2.5mm²
1.5 mm² is the smallest size returned for fixed wiring. Motor loads — air conditioners, pumps, compressors — pull two to three times their running current at start and normally get a dedicated circuit above this minimum. The job guides carry the size for each appliance.
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Sizing guidance, not a design. Have a licensed electrician confirm the size, the breaker and the earthing for your installation.
A design current of — needs more than 35 mm², or the run is long enough to push it there. We make copper armoured cable to 95 mm² and aluminium to 120 mm².
Every appliance fed by this cable, not just the biggest one. A 1.5 ton AC at 1500 W plus 200 W of lights is a 1700 W circuit.
Distance from the distribution board to the appliance, one way, following the route the cable takes — not the straight line across the room.
The result is the minimum for the load you entered. If more load will land on the same circuit later, take the next size up now.
The calculator holds three conditions at once and returns the smallest size that passes all three: it carries the current where it is installed, the volt drop stays inside the target, and a standard breaker fits between the load and the cable.
| Assumption | Value used |
|---|---|
| Supply voltage | 230 V single-phase · 400 V three-phase |
| Power factor | 1.0 when the load is entered in watts |
| Current capacity | BS 7671 method C (clipped direct), 30°C ambient, PVC insulated copper |
| Loaded conductors | 2 single-phase · 3 three-phase |
| Installation allowance | 1.00 clipped · 0.80 conduit or bunched · 0.70 hot roof or buried |
| Correction factors | The table figures are for clipped direct; the other two apply a flat first-pass allowance of 0.80 and 0.70, not the exact correction factors for your grouping and ambient. |
| Volt drop target | 2.5% — 5.75 V at 230 V, 10.00 V at 400 V |
| Volt drop figures | mV/A/m from the table; three-phase = 2-core figure × 0.866 |
| Breaker check | standard ratings 6–125 A, sized so Ib ≤ In ≤ Iz |
| Smallest size returned | 1.5 mm² (fixed wiring floor) |
| Range covered | 1.5 – 35 mm² copper |
| Not covered | aluminium conductors · DC strings and battery runs — for a solar DC run see the panel to inverter cable guide |
The same table the calculator reads. Current capacity is what the conductor carries clipped direct at 30°C — derate it for conduit, bunching and heat.
| Size | Single-phase | Three-phase | Volt drop | Typical use |
|---|---|---|---|---|
| 1.5 mm² | 19.5 A | 17.5 A | 29 mV/A/m | Lights, fans, small appliance sockets |
| 2.5 mm² | 27 A | 24 A | 18 mV/A/m | 1 ton AC, kitchen and utility sockets |
| 4 mm² | 36 A | 32 A | 11 mV/A/m | 1.5–2 ton AC, geyser |
| 6 mm² | 46 A | 41 A | 7.3 mV/A/m | 2 ton AC, AC side of a 3–5 kW inverter |
| 10 mm² | 63 A | 57 A | 4.4 mV/A/m | Main connection, AC side of a 5–10 kW inverter |
| 16 mm² | 85 A | 76 A | 2.8 mV/A/m | Commercial supply, AC side of a 10–15 kW inverter |
| 25 mm² | 112 A | 96 A | 1.75 mV/A/m | Submains and 3-phase feeders |
| 35 mm² | 138 A | 119 A | 1.25 mV/A/m | Large industrial feeders |
Send the size, the length in meters and your city. We quote the factory rate for that day and dispatch — Punjab in 1–2 days, rest of Pakistan in 2–4.