{ "name": "Voltage Drop Calculator", "url": "https://calculators.geekmidst.com/calculators/voltage-drop-calculator", "markdown": "https://calculators.geekmidst.com/calculators/voltage-drop-calculator.md", "category": "Science & engineering", "description": "Estimate the voltage drop along a copper or aluminium cable from its size (mm² or AWG), length and current, for DC, single-phase or three-phase.", "summary": "Current flowing through a cable’s resistance loses some voltage before it reaches the load. The drop grows with current and length and falls as the conductor gets thicker.", "also_called": [ "Cable voltage drop calculator", "Wire voltage drop calculator" ], "applies_to": "Worldwide", "last_updated": "2026-10-29", "computation": "Results are computed in the visitor’s browser on the HTML page. This API describes the calculator; it does not compute results.", "inputs": [ { "name": "system", "label": "System", "type": "select", "default": "single", "options": { "dc": "DC (two wires)", "single": "Single-phase AC", "three": "Three-phase AC (balanced)" } }, { "name": "voltage", "label": "Supply voltage", "type": "number", "default": "230", "unit": "V" }, { "name": "current", "label": "Load current", "type": "number", "default": "16", "unit": "A" }, { "name": "length", "label": "One-way cable length", "type": "number", "default": "30" }, { "name": "length_unit", "label": "Length in", "type": "segmented", "default": "m", "options": { "m": "Metres", "ft": "Feet" } }, { "name": "size_type", "label": "Conductor size as", "type": "segmented", "default": "mm2", "options": { "mm2": "mm²", "awg": "AWG" } }, { "name": "area", "label": "Conductor cross-section", "type": "number", "default": "2.5", "unit": "mm²", "shown_when": { "size_type": "mm2" } }, { "name": "awg", "label": "Wire gauge", "type": "select", "default": "12", "options": { "4/0": "4/0 AWG", "3/0": "3/0 AWG", "2/0": "2/0 AWG", "1/0": "1/0 AWG", "1": "1 AWG", "2": "2 AWG", "3": "3 AWG", "4": "4 AWG", "6": "6 AWG", "8": "8 AWG", "10": "10 AWG", "12": "12 AWG", "14": "14 AWG", "16": "16 AWG", "18": "18 AWG", "20": "20 AWG", "22": "22 AWG", "24": "24 AWG" }, "shown_when": { "size_type": "awg" } }, { "name": "material", "label": "Conductor", "type": "segmented", "default": "copper", "options": { "copper": "Copper", "aluminium": "Aluminium" } }, { "name": "temperature", "label": "Conductor temperature", "type": "number", "default": "20", "unit": "°C", "optional": true } ], "outputs": [ { "key": "drop_volts", "label": "Voltage drop", "format": "number" }, { "key": "drop_percent", "label": "Drop as a share of supply", "format": "percent" }, { "key": "load_voltage", "label": "Voltage at the load", "format": "number" }, { "key": "conductor_area", "label": "Conductor cross-section", "format": "number" }, { "key": "ohm_per_km", "label": "Conductor resistance", "format": "number" }, { "key": "loss_watts", "label": "Power lost in the cable", "format": "number" } ], "formula": { "text": "R = ρ × L ÷ A × (1 + α(T − 20 °C)); DC and single-phase: Vd = 2 × I × R; three-phase: Vd = √3 × I × R", "variables": { "ρ": "resistivity at 20 °C: copper 0.017241 Ω·mm²/m (1/58, 100% IACS), aluminium 0.028265 (61% IACS)", "L": "one-way length (m)", "A": "cross-section (mm²); AWG uses d = 0.127 mm × 92^((36 − n)/39)", "α": "temperature coefficient: copper 0.00393, aluminium 0.00403 per °C", "I": "load current (A)" } }, "worked_example": { "inputs": { "system": "single", "voltage": "230", "current": "16", "length": "30", "length_unit": "m", "size_type": "mm2", "area": "2.5", "awg": "12", "material": "copper", "temperature": "20" }, "steps": [ "Resistance of one conductor: 0.017241 × 30 ÷ 2.5 = 0.2069 Ω.", "Single-phase current flows out and back: Vd = 2 × 16 × 0.2069 = 6.62 V.", "6.62 ÷ 230 = 2.88% of the supply, leaving 223.38 V at the load." ], "result": "16 A over 30 m of 2.5 mm² copper drops about 6.6 V (2.9%) on a 230 V single-phase circuit at 20 °C." }, "interpretation": "Wiring rules set maximum drops, often a few per cent depending on the country and the type of circuit. If the result is close to your limit, use a larger conductor or a shorter route, and repeat the calculation at the cable’s operating temperature.", "assumptions": [ "Resistive drop only: cable reactance and load power factor are ignored, which is accurate for small and medium cables at mains frequency.", "Three-phase loads are balanced." ], "limitations": [ "Cable sizing must also meet current-carrying capacity, fault protection and installation rules set by your local wiring regulations.", "Very large conductors (above about 50 mm²) need reactance included; use the manufacturer’s mV/A/m data." ], "rules": null, "faqs": [ { "question": "Why multiply by 2 for single-phase?", "answer": "Current goes out along one conductor and returns along the other, so the cable length is effectively doubled. In a balanced three-phase circuit the factor is √3 instead." }, { "question": "Which temperature should I use?", "answer": "For a quick check use 20 °C. For a design check use the cable’s maximum operating temperature (for example 70 °C for PVC insulation), which raises copper resistance by about 20%." } ], "sources": [], "related": [ { "name": "Ohm’s Law Calculator", "url": "https://calculators.geekmidst.com/calculators/ohms-law-calculator" }, { "name": "Resistor Calculator", "url": "https://calculators.geekmidst.com/calculators/resistor-calculator" }, { "name": "Length Converter", "url": "https://calculators.geekmidst.com/calculators/length-converter" } ], "disclaimer": "Quantities are estimates. Confirm requirements with your engineer or supplier before ordering materials.", "publisher": "GM¹X CalcVerse" }