⚡ Electrical Calculator PRO
Wire size, voltage drop, panel load, conduit fill & NEC compliance.
Circuit Diagram — updates as you type
Longer runs and heavier loads push voltage drop up — the wire gauge below is sized to hold it within limits.
1 Circuit Type
2 Electrical Specs
3 Loads
4 Panel Info (Optional)
5 Cost & Details
Labour Cost
Results
Load Analysis
Wire Sizing (NEC)
Voltage Drop
Conduit Fill
Panel Check
Breaker & Protection
⚠️ Pre-Export Checklist
- All loads accounted for
- Wire gauge verified per NEC 310.15
- Voltage drop within acceptable limits
- Conduit fill ≤ 40%
- Panel capacity sufficient
- GFCI/AFCI requirements checked
- Electrical permit obtained
- Licensed electrician on-site
Professional Electrical Sizing Guide
Show NEC tables, formulas & pro tips ▼
NEC Wire Ampacity Table (THHN, 30°C)
| AWG | Amps | Diameter | Weight/ft |
|---|---|---|---|
| 14 | 20A | 0.0641" | 0.034 lb |
| 12 | 25A | 0.0808" | 0.052 lb |
| 10 | 35A | 0.1019" | 0.082 lb |
| 8 | 50A | 0.1285" | 0.131 lb |
| 6 | 65A | 0.1620" | 0.207 lb |
| 4 | 85A | 0.2043" | 0.329 lb |
| 3 | 100A | 0.2293" | 0.415 lb |
| 2 | 115A | 0.2576" | 0.523 lb |
| 1 | 130A | 0.2893" | 0.660 lb |
Formulas
Amps = Watts ÷ Voltage (single phase)
Amps (3-phase) = Watts ÷ (Voltage × √3 × PF)
Voltage Drop = (2 × Length × Amps × Resistance) ÷ 1000
V Drop %= (Voltage Drop ÷ Supply Voltage) × 100
Conduit Fill = (Wire Area × Conductors) ÷ Conduit Area × 100
Common Mistakes to Avoid
- Ignoring voltage drop — over 3% is unacceptable per NEC
- Using wrong ampacity for temperature — higher temp = derate wire
- Undersizing ground wire — always match or exceed grounding rules
- Not GFCI-protecting wet locations (kitchen, bath, outdoor, garage)
- Mixing wire types in same conduit without derating
Pro Tips
- Always upsize wire for runs >50 ft to control voltage drop
- Use #12 AWG minimum for 20A kitchen/bathroom circuits
- THHN in conduit, NM-B (Romex) in dry residential walls
- Keep conduit fill under 40% for easy wire pulls
- Label all circuits at the panel — saves hours of troubleshooting
Electrical — 3D Preview
Drag to rotate — Scroll to zoom
İlgili Hesaplayıcılar
Frequently used together on the same project.
Client & Quote (prints on PDF & Excel)
Adjustments (applies to exports)
Contingency is added as a separate line on the exported cost summary. Waste % is printed as an advisory reminder.
Project notes (prints on PDF & Excel)
Result compare (A/B)
| Item | Pinned | Current | Change |
|---|---|---|---|
Saved rates auto-apply from your Price Library. Advanced details stay in your browser — nothing is uploaded except inside your own PDF/Excel exports.
Electrical work demands precision. An undersized wire can overheat and start a fire, while oversized wire wastes money on copper you do not need. Our free online electrical calculator helps homeowners and electricians quickly determine wire gauge, circuit breaker sizing, conduit requirements, and total material cost for residential and light commercial wiring projects.
Whether you are wiring a new room addition, upgrading a panel, or running circuits to outlets and switches, this tool provides the calculations you need in seconds. The calculator starts with your total connected load in watts or kilowatts, then applies the NEC 80 percent rule for continuous loads to determine the required amperage. From there it recommends the appropriate wire gauge — for example, 12 AWG copper for 20-amp circuits and 14 AWG for 15-amp circuits. It also calculates voltage drop over distance, which is critical for long runs to outbuildings or detached garages.
The conduit sizing feature ensures your wire fits inside the raceway with room for future additions. Cost estimation covers wire, conduit, boxes, breakers, and miscellaneous fittings. We have used this tool on hundreds of residential projects and it consistently delivers accurate material lists that match what the inspector wants to see.
📖 Bu Elektrik Hesaplayıcı Nasıl Kullanılır
Step 1: List All Loads
Enter the total wattage of all devices on the circuit. Add up lights, outlets, appliances, and motors. For kitchen circuits, assume 1,500 watts per small-appliance branch circuit.
Step 2: Select Voltage
Choose 120V for standard outlets and lighting, 240V for large appliances like dryers and ranges, or three-phase for commercial equipment.
Step 3: Enter Circuit Length
Measure the distance from the panel to the farthest outlet on the circuit. Long runs cause voltage drop — the calculator flags circuits that exceed the 3% NEC recommendation.
Step 4: Choose Wire Type
Select Romex (NM-B) for residential dry locations, MC cable for commercial, or conduit with individual wires for exposed or underground runs.
Step 5: Enter Material Costs
Input per-foot pricing for wire and conduit, plus per-unit costs for boxes, breakers, and fittings. The calculator totals everything.
Step 6: Review Results
The output includes required amperage, recommended wire gauge, conduit size, breaker rating, and total estimated cost.
📐 Elektrik Yük Formülü
The fundamental electrical formula is Current (Amps) = Power (Watts) / Voltage. For a 15-amp circuit at 120 volts, the maximum continuous load is 15 × 0.8 = 12 amps (following the NEC 80% rule), which equals 1,440 watts. For a 20-amp circuit, the continuous load limit is 20 × 0.8 = 16 amps or 1,920 watts.
Wire sizing depends on amperage and run length. For copper wire: 14 AWG handles up to 15 amps, 12 AWG handles up to 20 amps, and 10 AWG handles up to 30 amps. Voltage drop is calculated as VD = (2 × L × I × R) / 1000, where L is the one-way circuit length in feet, I is the current in amps, and R is the resistance per 1,000 feet. The NEC recommends keeping voltage drop below 3% for branch circuits.
For example, a 20-amp kitchen circuit with 2,400 watts of load at 120 volts draws 20 amps. At 80% continuous load rating, you should upsize to a 30-amp circuit or keep the load under 1,920 watts on a 20-amp breaker. For a 75-foot run using 12 AWG copper, the voltage drop is 4.8 volts, or 4% of 120V. Since that exceeds the 3% recommendation, you would upsize to 10 AWG for that run.
⚠️ Kaçınılacak Hatalar
Ignoring the NEC 80% continuous load rule
✓ A 20-amp circuit should not carry more than 16 amps of continuous load. Exceeding this trips breakers and creates fire hazards.
Not calculating voltage drop on long runs
✓ Over 75 feet, voltage drop can exceed 3%, causing lights to dim and motors to overheat. Upsize the wire for runs over 100 feet.
Mixing wire gauge on a circuit
✓ The entire circuit must use the same wire gauge as rated by the breaker. Mixing 12 AWG and 14 AWG on a 20-amp circuit is a code violation.
Oversizing conduit without reason
✓ The NEC limits conduit fill to 40% for three or more wires. Oversized conduit wastes money and makes wire pulling harder.
Not accounting for derating in hot environments
✓ In attics or enclosed spaces above 86F, wire ampacity must be derated. This may require upsizing the wire for the same circuit load.
💡 Profesyonel İpuçları
Run a dedicated 20-amp circuit for each kitchen small-appliance area. The NEC requires at least two 20-amp circuits for kitchen countertop receptacles.
Use wire nuts rated for the number of conductors. A three-way wire nut on four wires will not make a reliable connection.
Label every circuit at the panel during installation. Six months from now, you will not remember which breaker controls which room.
Install AFCI breakers in bedrooms, living rooms, and other habitable rooms as required by the NEC.
For outdoor runs, use UF-B cable rated for direct burial. Standard Romex is not rated for wet or buried locations.
❓ Sık Sorular
A 20-amp circuit requires 12 AWG copper wire (NM-B Romex for residential). For runs over 75 feet, consider upsizing to 10 AWG to minimize voltage drop. Never use 14 AWG wire on a 20-amp breaker.
The NEC does not limit the number of outlets on a residential branch circuit, but practical limits are 8 to 10 outlets per 15-amp circuit. Kitchen and bathroom circuits must be dedicated.
Most jurisdictions require a permit for new circuits, panel upgrades, or any work beyond simple device replacement. Permits typically cost 50 to 200 dollars.
12 AWG wire is rated for 20 amps and is required for kitchen, bathroom, laundry, and garage circuits. 14 AWG wire is rated for 15 amps for general lighting and bedroom circuits.
🏗️ Gerçek Uygulamalar
Electrical material estimation is critical because mistakes are expensive and dangerous. For a typical room addition with four outlets, two light switches, and a ceiling fan, the wiring material cost runs 200 to 400 dollars, but incorrect wire sizing or circuit loading can lead to failed inspections or fire hazards.
Residential panel upgrades are one of the most common electrical projects. Going from a 100-amp to a 200-amp panel typically costs 1,500 to 3,000 dollars in materials. Commercial electrical work requires even more precise estimation. A typical office buildout might include 50 to 100 receptacles, 20 to 30 lighting circuits, and dedicated circuits for HVAC equipment.
Our free electrical calculator is the most accurate online tool for estimating wire gauge, circuit breaker sizing, conduit requirements, and electrical material costs. All calculations follow NEC guidelines for safe, code-compliant installations.
✅Method, Sources & Review
Maintained by theBuildingCalc methods desk· Last reviewedSeptember 23, 2026. This calculator implements the standards and references below; every figure can be rechecked against the formulas and worked example on this page.
Results are estimates, not engineering advice. Verify against local codes and licensed professionals for structural, electrical, and gas work. See ourTerms. Spotted an error? Report it— corrections ship with the next review.