Wire & Cable Calculator | Electrical Sizing Tool
This wire and cable calculator helps you select the correct conductor size based on voltage drop, current, distance, and material. Calculate wire gauge (AWG/mm²), voltage drop percentage, resistance, power loss, and ampacity for DC, single-phase, and three-phase systems. Includes Ohm's Law tool and NEC/IEC compliance considerations for safe electrical installations.
Wire & Cable Calculator | Wire Gauge, Voltage Drop & Cable Sizing
Calculate the correct wire gauge and cable size for safe, efficient electrical installations with accurate voltage drop planning for residential and industrial use.
Wire Calculator (Voltage Drop + Wire Size + AWG↔mm²)
Plan safer wiring for 12V DC, 240V AC, single-phase or three-phase: voltage drop, resistance, power loss, and a practical wire-size suggestion (AWG + mm²).
Planning Inputs
Enter what you know. The tool validates and calculates instantly.
Utilities (Conversion + Ohm’s Law)
Quick helpers to reduce mistakes.
Analysis & Results
Transparent outputs + formulas + visuals.
Visual: Voltage Drop vs Wire Size
Bar chart shows VD% for common sizes.
| Size | Area (mm²) | Resistance (Ω/km) | VD (V) | VD (%) | Power Loss (W) | Ampacity (A)† | Pass (VD%) |
|---|---|---|---|---|---|---|---|
| No results yet. | |||||||
Formulas Used (MathJax / LaTeX)
Shown for transparency. Units are critical.
Notation: \(I\) current (A), \(L\) one-way length (m), \(R_{\text{km}}\) resistance (Ω/km), \(V\) supply (V), \(pf=\cos\varphi\).
Note: This tool uses a practical resistance table and simplified AC assumptions (reactance is not modeled). Always verify against local electrical code tables and installation conditions.
Copy-Friendly Report Preview
What will be copied to your clipboard.
Accuracy note: Results are estimates based on typical conductor resistance values at ~20°C with an optional temperature adjustment. For compliance (NEC/IEC) and final sizing, consult a qualified electrician and your local code requirements.
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Wire & Cable Calculator: Complete User Guide
Professional Electrical Calculations Made Simple
📋 How to Use the Calculator: Step-by-Step Guide
1 Planning Inputs Section
Location: Left panel of the calculator
System Configuration:
- System Type: Choose DC, AC Single-Phase, or AC Three-Phase
- Supply Voltage: Enter voltage in volts (V)
- Load Current: Enter current in amperes (A)
- Load Type: Select continuous (≥3 hours) or non-continuous
2 Distance and Material Settings
Critical Parameters:
- One-Way Distance: Enter the single-direction wire run length
- Distance Unit: Select meters (m), feet (ft), or kilometers (km)
- Conductor Material: Choose Copper (Cu) or Aluminum (Al)
- Ambient Temperature: Enter working environment temperature in °C
3 Voltage Drop and Advanced Settings
Performance Targets:
- Allowed Voltage Drop: Enter maximum percentage drop (typically 3-5%)
- Power Factor: For AC systems, enter 0.1-1.0 (blank = 1.0 assumed)
- Conductor Count: Number of current-carrying conductors for derating notes
🔬 Formulas Used in Calculations
1. Resistance Temperature Adjustment
Conductor resistance changes with temperature:
\[ R(T) = R(20^\circ C) \times [1 + \alpha \times (T - 20)] \]Where:
- R(T) = Resistance at temperature T (Ω/km)
- R(20°C) = Base resistance at 20°C (Ω/km)
- α = Temperature coefficient (Cu: 0.00393/°C, Al: 0.00403/°C)
- T = Ambient temperature (°C)
2. Path Resistance Calculation
Total circuit resistance depends on system type:
\[ \begin{aligned} L_{\text{km}} &= \frac{L_{\text{m}}}{1000} \\ R_{\text{path}} &= \begin{cases} 2 \times R_{\text{km}} \times L_{\text{km}} & \text{(DC \& Single-Phase AC)} \\ R_{\text{km}} \times L_{\text{km}} & \text{(Three-Phase AC, line-to-line)} \end{cases} \end{aligned} \]Where:
- Lₖₘ = Length in kilometers (km)
- Rₖₘ = Conductor resistance per km (Ω/km)
3. Voltage Drop Formulas
Different calculations for each system type:
\[ \begin{aligned} \Delta V_{\text{DC}} &= I \times R_{\text{path}} \\ \Delta V_{\text{1φ}} &= I \times R_{\text{path}} \\ \Delta V_{\text{3φ}} &= \sqrt{3} \times I \times (R_{\text{km}} \times L_{\text{km}}) \times \cos\varphi \end{aligned} \]Where:
- ΔV = Voltage drop (V)
- I = Current (A)
- cosφ = Power factor
4. Percentage Voltage Drop and Power Loss
\[ \begin{aligned} \%\Delta V &= 100 \times \frac{\Delta V}{V_{\text{supply}}} \\ P_{\text{loss}} &= I^2 \times R_{\text{path}} \end{aligned} \]Where:
- %ΔV = Voltage drop percentage
- Vₛᵤₚₚₗᵧ = Supply voltage (V)
- Pₗₒₛₛ = Power loss in conductors (W)
📊 Wire Size Comparison Table
Standard AWG to mm² Conversion Reference:
| AWG Size | Cross-Section (mm²) | Resistance (Ω/km) at 20°C | Typical Ampacity* | Max Current (90°C THHN) |
|---|---|---|---|---|
| 14 | 2.08 | 8.286 | 15 A | 25 A |
| 12 | 3.31 | 5.211 | 20 A | 30 A |
| 10 | 5.26 | 3.277 | 30 A | 40 A |
| 8 | 8.37 | 2.061 | 40 A | 55 A |
| 6 | 13.3 | 1.296 | 55 A | 75 A |
| 4 | 21.2 | 0.815 | 70 A | 95 A |
| 2 | 33.6 | 0.513 | 95 A | 130 A |
| 1/0 | 53.5 | 0.323 | 125 A | 170 A |
| 3/0 | 85.0 | 0.203 | 165 A | 225 A |
*Ampacity values are for reference only. Always consult NEC/IEC tables for final sizing based on installation conditions, insulation type, and ambient temperature.
⚡ How Do You Calculate Wire Size?
Fundamental Wire Sizing Principles
Wire size calculation involves balancing three critical factors:
- Ampacity Requirements: The wire must safely carry the load current without overheating
- Voltage Drop Limits: The voltage at the load must remain within acceptable limits
- Short Circuit Protection: The wire must be protected by appropriate overcurrent devices
Basic Wire Size Calculation Steps:
- Determine Load Current: Calculate or measure the full load current (FLA)
- Apply Correction Factors: Adjust for temperature, bundling, and continuous operation
- Calculate Voltage Drop: Ensure voltage drop is within acceptable limits (typically 3-5%)
- Select Wire Size: Choose the smallest wire that meets both ampacity and voltage drop requirements
🔌 Calculating Wire Sizes for Three-Phase AC Systems
Three-Phase Specific Considerations
Three-phase systems have unique characteristics that affect wire sizing:
Three-Phase Voltage Drop Formula:
\[ \Delta V_{3\phi} = \sqrt{3} \times I \times L \times R \times \cos\varphi \]Where:
- ΔV₃φ = Voltage drop (V)
- I = Line current (A)
- L = One-way length (m)
- R = Resistance per unit length (Ω/m)
- cosφ = Power factor
Key Differences from Single-Phase:
- √3 Factor: Three-phase systems use √3 (approximately 1.732) in calculations
- Lower Current: For the same power, three-phase currents are lower than single-phase
- Power Factor Critical: Power factor has significant impact on voltage drop
- Neutral Sizing: For balanced loads, neutral may be sized smaller than phase conductors
🌡️ Correcting for Operating Temperature
Temperature Correction Factors
Wire resistance increases with temperature, affecting both voltage drop and ampacity:
Resistance Temperature Correction:
\[ R_T = R_{20} \times [1 + \alpha \times (T - 20)] \]Where:
- R_T = Resistance at temperature T (Ω/km)
- R₂₀ = Resistance at 20°C (Ω/km)
- α = Temperature coefficient (Cu: 0.00393/°C, Al: 0.00403/°C)
- T = Actual operating temperature (°C)
Common Temperature Correction Factors:
| Ambient Temperature (°C) | Copper Correction | Aluminum Correction | Ampacity Derating |
|---|---|---|---|
| 20 | 1.00 | 1.00 | 100% |
| 30 | 1.04 | 1.04 | 94% |
| 40 | 1.08 | 1.08 | 88% |
| 50 | 1.12 | 1.12 | 82% |
| 60 | 1.16 | 1.16 | 75% |
📱 How to Use This Electrical Wire Size Calculator
Practical Calculator Walkthrough
Follow these steps for accurate wire sizing calculations:
Step 1: Enter Basic Parameters
- Select your system type (DC, AC Single-Phase, or AC Three-Phase)
- Enter the supply voltage (e.g., 120V, 240V, 480V)
- Input the load current in amperes
- Specify if the load is continuous (runs 3+ hours)
Step 2: Define Installation Conditions
- Enter the one-way distance from source to load
- Select the appropriate distance unit
- Choose conductor material (Copper or Aluminum)
- Input ambient temperature for accurate resistance calculation
Step 3: Set Performance Targets
- Define maximum allowed voltage drop percentage (typically 3-5%)
- For AC systems, enter power factor if known
- Specify number of current-carrying conductors for derating notes
Step 4: Calculate and Review
- Click "Calculate" to generate results
- Review the recommended wire size in both AWG and mm²
- Check voltage drop percentage against your limit
- Examine power loss and efficiency calculations
🔍 Example: Using This AC Wire Size Calculator
Practical Calculation Example
Scenario: Installing a 240V single-phase workshop circuit
Given Parameters:
- System Type: AC Single-Phase
- Supply Voltage: 240 V
- Load Current: 30 A
- Load Type: Continuous (power tools running for hours)
- One-Way Distance: 25 meters
- Conductor Material: Copper
- Ambient Temperature: 30°C
- Voltage Drop Limit: 3%
Calculation Steps Performed by the Calculator:
1. Adjust for Continuous Load:
\[ I_{\text{design}} = 30 \times 1.25 = 37.5 \text{ A} \]2. Calculate Path Resistance:
\[ \begin{aligned} L_{\text{km}} &= 25 / 1000 = 0.025 \text{ km} \\ R_{\text{path}} &= 2 \times R_{\text{km}} \times L_{\text{km}} \end{aligned} \]3. Determine Wire Size:
The calculator iterates through wire sizes to find the smallest that meets both ampacity and voltage drop requirements.
Expected Results:
- Recommended Wire: AWG 6 (13.3 mm²)
- Voltage Drop: Approximately 2.8% (within 3% limit)
- Power Loss: ~65 Watts
- Wire Resistance: ~0.065 Ω (round trip)
📈 Visual Guide: Voltage Drop vs Wire Size
Understanding the Chart:
The calculator generates a bar chart showing voltage drop percentage for different wire sizes. The red dashed line represents your specified voltage drop limit. Bars below this line meet your requirements.
🎯 Input Validation and Error Prevention
Automatic Validation Checks:
- Voltage: Must be > 0 V
- Current: Must be > 0 A
- Distance: Must be > 0 in selected units
- Power Factor: Must be between 0.1 and 1.0 for AC systems
- Voltage Drop Limit: Must be between 0% and 20%
- Temperature: Valid range: -50°C to +200°C
⚡ Ohm's Law Utility Section
Quick Electrical Calculations
The calculator includes an Ohm's Law solver for quick conversions:
\[ \begin{aligned} V &= I \times R \\ P &= V \times I \\ P &= I^2 \times R \\ P &= \frac{V^2}{R} \end{aligned} \]📝 Accuracy and Limitations
Accuracy Statement
This calculator provides engineering estimates based on standard resistivity values:
- Copper: 1.724×10⁻⁸ Ω·m at 20°C
- Aluminum: 2.65×10⁻⁸ Ω·m at 20°C
Key Limitations:
- Reactance not modeled: AC calculations assume resistance-only; actual AC impedance includes inductive reactance
- Simplified temperature model: Uses linear coefficient; actual behavior is more complex
- Standard conditions: Based on free air, single conductors; bundling effects are noted but not calculated
- Ampacity reference only: Ampacity values are for comparison; not code-compliant without derating
⚠️ Disclaimer
Important Legal and Safety Notice
This wire calculator is intended for preliminary planning and educational purposes only.
Not for Final Design: The results provided by this calculator are estimates based on simplified models and typical conditions. They do not constitute professional engineering advice.
Code Compliance Required: All electrical installations must comply with local electrical codes (NEC, IEC, CEC, etc.) and regulations. This calculator does not guarantee code compliance.
Professional Verification Essential: Always have final wire sizing and electrical designs reviewed and approved by a qualified, licensed electrician or professional engineer.
Safety First: Electrical work can be dangerous. If you are not qualified, do not attempt electrical installations. Contact a licensed professional.
No Liability: The creators of this calculator accept no liability for damages, injuries, or code violations resulting from the use of this tool.
❓ Frequently Asked Questions (FAQs)
▶ How do I calculate wire size for motors?
For motor circuits, consider:
- Full Load Current (FLA): From motor nameplate or NEC Table 430.250
- Starting Current: Typically 6× FLA - check for voltage drop during start
- Continuous Duty: Motors are typically continuous loads (apply 125% factor)
- Power Factor: Motor loads often have 0.8-0.9 power factor
- Temperature Rating: Consider motor operating temperature
Example: For a 5 HP, 240V single-phase motor (FLA = 28A), design current = 28 × 1.25 = 35A.
▶ How do I calculate wire size for 3 phase?
Three-phase calculations differ in several ways:
- Use √3 factor: Voltage drop formula includes √3 (approximately 1.732)
- Lower Current: For same power, 3-phase current = Single-phase current ÷ √3
- Line vs Phase: Ensure you're using line current and line-to-line voltage
- Neutral Sizing: For balanced loads, neutral may be smaller; for unbalanced, same size
Formula: \( \Delta V = \sqrt{3} \times I \times L \times R \times \cos\varphi \)
▶ How do I calculate AWG wire size?
AWG (American Wire Gauge) sizes follow specific rules:
- Smaller Number = Larger Wire: AWG 10 is larger than AWG 12
- Geometric Progression: Each 3 AWG sizes doubles/halves cross-sectional area
- Resistance Calculation: Resistance increases as AWG number increases
- Common Conversions:
- AWG 14 = 2.08 mm²
- AWG 12 = 3.31 mm²
- AWG 10 = 5.26 mm²
- AWG 8 = 8.37 mm²
Use the calculator's AWG ↔ mm² converter for precise conversions.
▶ How do I calculate wire size for distance?
For long-distance runs, voltage drop becomes the controlling factor:
- Determine Acceptable Drop: Typically 3-5% of supply voltage
- Calculate Maximum Resistance: \( R_{\text{max}} = \frac{\Delta V_{\text{max}}}{I} \)
- Find Wire Size: Select wire with resistance ≤ \( R_{\text{max}} ÷ (2 × L) \) for DC/single-phase
- Consider Temperature: Adjust resistance for operating temperature
- Check Ampacity: Ensure wire can still carry the current safely
Rule of thumb: For every doubling of distance, you may need to increase wire size by 1-2 AWG numbers.
🔧 Common Use Cases and Examples
Typical Applications:
1. Solar PV Systems (12V/24V DC)
- Inputs: 12V DC, 10A continuous, 15m distance, 3% VD limit
- Typical Result: Recommends AWG 8 (8.37 mm²)
- Microcopy Tip: Use "Continuous" load type for solar applications
2. Home Workshop (240V Single-Phase)
- Inputs: 240V AC single-phase, 30A, 25m, 3% VD limit
- Typical Result: Recommends AWG 6 (13.3 mm²)
- Microcopy Tip: Include power factor for motor loads (typically 0.8-0.9)
3. Industrial Motor (480V Three-Phase)
- Inputs: 480V AC three-phase, 50A, 40m, 5% VD limit, PF=0.85
- Typical Result: Recommends AWG 4 (21.2 mm²)
🚀 Pro Tips for Best Results
- Start with Example: Use the "Load Example" button to see proper formatting
- Project Naming: Name your projects for easy reference in reports
- Use Notes Field: Document special conditions (outdoor, conduit type, local code requirements)
- Copy Reports: Use "Copy Full Report" to save calculations for permits or client documentation
- Check Warnings: Always read warning messages for important safety notes
- Temperature Matters: For hot environments (attics, engine rooms), increase ambient temperature input
- Aluminum Considerations: When using aluminum, remember it requires larger sizes and special terminations
- Future Expansion: Consider upsizing for potential future load increases
- Verify with Tables: Cross-check results with NEC/IEC ampacity tables
- Professional Review: Always have final designs reviewed by a qualified electrician
Ready to Calculate?
Return to the Wire & Cable Calculator and start planning your electrical projects with confidence!
Last Updated: | Calculator Version: 2.1 | Professional Electrical Tool
