This calculator estimates the voltage drop in a wire due to resistance when current flows through it.
The Voltage Drop Calculator is an essential tool for electricians, engineers, and DIY enthusiasts who want to ensure efficient electrical system design. Voltage drop occurs when the voltage at the end of a cable run is lower than at the beginning, due to the resistance in the wire. Understanding and calculating this voltage loss is critical for maintaining safety, performance, and compliance with electrical codes.
Voltage drop is the reduction in voltage as electrical current travels through a wire or cable. It is caused by the inherent resistance (or impedance) of the conductor. This loss becomes especially significant over long distances or when using cables with insufficient thickness for the given load.
Formula:
Voltage Drop (V) = (2 × L × I × R) / 1000
The "2" accounts for the round trip (to and from the load).
Excessive voltage drop can lead to motor failures, dim lighting, poor appliance performance, and increased power consumption.
Regulations usually specify acceptable limits for voltage drop:
| Conductor | Resistance (Ω/km) |
|---|---|
| Copper | 0.0175 |
| Aluminum | 0.0282 |
Values vary slightly based on temperature and wire quality.
Let’s say you’re powering a 240V water pump 100 meters away using copper cable, drawing 20A of current. Wire resistance is 0.0175 ohm/km.
Voltage Drop = (2 × 100 × 20 × 0.0175) / 1000 = 0.07V
Voltage at load = 240 - 0.07 = 239.93V — well within limits.
| Voltage Drop (%) | Result Interpretation |
|---|---|
| < 3% | ✅ Ideal for branch circuits |
| 3% – 5% | ⚠️ Acceptable for feeders (check total system) |
| > 5% | ❌ Exceeds safe limits – use thicker cable |
A: Yes. Persistent low voltage can overheat motors, reduce appliance lifespan, and create erratic behavior in electronics.
A: For most residential and commercial applications, ≤ 3% per branch and ≤ 5% total drop is the accepted standard.
A: Yes, it works for both AC and DC, though DC systems often require lower voltage drops due to lack of regulation tolerance.
A: Higher temperatures increase conductor resistance, which increases voltage drop. For high-temperature areas, consider upsizing cable.
Once you calculate voltage drop, you can estimate power loss using:
Power Loss (W) = Voltage Drop × Current
This helps determine energy waste over time, especially in industrial or solar setups.
The Voltage Drop Calculator ensures that your electrical designs are both safe and efficient. With just a few inputs, you can avoid common mistakes like under-sizing wires or overloading circuits. It’s an indispensable tool for planning, troubleshooting, and upgrading any electrical system.
⚡ Don’t risk device damage or non-compliance. Use our calculator to stay within limits and optimize every connection.
Voltage drop behaves differently in various electrical systems. While the underlying principle remains the same, application and tolerance levels vary depending on whether the system is residential, commercial, or industrial.
Our calculator is adaptable to single-phase and three-phase systems and supports both copper and aluminum conductors. It provides quick, actionable results for electrical planners across all sectors.
In a three-phase system, voltage drop is calculated differently than in single-phase. The general formula for line-to-line three-phase voltage drop is:
Voltage Drop = (√3 × L × I × R) / 1000
This formula accounts for the balanced nature of three-phase power. The use of √3 (approximately 1.732) ensures correct adjustment for phase difference.
Tip: Use three-phase settings in the calculator if your load and source are both part of a three-phase system, common in industrial or commercial buildings.
Incorrect wire sizing is one of the most common causes of voltage drop. Here’s how choosing the right wire size helps reduce the issue:
| Wire Size (mm²) | Approx. Resistance (Ω/km) | Usage |
|---|---|---|
| 1.5 mm² | 12.1 | Lighting circuits |
| 2.5 mm² | 7.41 | Socket outlets |
| 6 mm² | 3.08 | Water heaters, AC |
| 10 mm² | 1.83 | High-load equipment |
The calculator helps you test different wire sizes instantly to meet the allowed voltage drop percentage.
Voltage drop is more significant in low voltage systems because a small drop represents a larger percentage loss. For example, a 5V drop in a 230V system is only ~2%, but in a 12V system it is over 40%!
Use this tool for low-voltage applications like off-grid solar setups or caravan lighting, where voltage drop matters even more than in regular household wiring.
Solar installers must keep voltage drop to a minimum, especially between the solar panels, charge controller, and battery bank. Here’s what to keep in mind:
Even 1V of drop in a 12V system could make the difference between fully charging a battery or not. Our calculator helps avoid such losses with ease.
Wire resistance increases with temperature. For every 1°C rise in temperature, resistance in copper increases by about 0.393%.
Formula: R = R0 × [1 + α × (T - T0)]
When calculating voltage drop for environments like rooftops or engine bays, increase your safety margin or choose larger cables.
Did you know that long extension cords can cause voltage drop that affects device performance? Many users overload thin extension wires, especially for power tools or air conditioners, which can result in overheating or motor burnout.
Use Case: A 30-meter cord with a 1.5 mm² wire powering a 2,000W tool at 230V = ~8.7 Amps
Voltage Drop ≈ 2 × 30 × 8.7 × 0.0121 = 6.3V → Device receives only 223.7V
Use our calculator to test voltage drop before choosing extension cord length and thickness.
Voltage drop not only reduces performance — it wastes energy. Here’s how you calculate that waste:
Energy Loss (kWh/year) = Vdrop × I × H / 1000
For a voltage drop of 5V, current of 20A, and 2,000 hours/year:
5 × 20 × 2000 / 1000 = 200 kWh/year
At ₹10/unit, that's ₹2,000/year lost due to poor wiring choices — something you can fix using this calculator.
The Voltage Drop Calculator is more than just a number cruncher. It’s a decision-making tool for safety, efficiency, and cost-saving. Whether you're working on a home installation, a solar farm, or a factory expansion — calculating voltage drop ahead of time ensures better performance and compliance.
📌 Start calculating now and avoid costly mistakes later. Optimize your design, cut energy losses, and protect your equipment — all with just a few clicks.