⚡ 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
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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.
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⚠️ 应避免的常见错误
估算时未将英寸转换为英尺
✓ 确保所有尺寸使用相同单位。
忽略损耗系数
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材料计算不准确
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💡 专业提示
始终订购超出计算量的材料。
检查当地建筑规范。
提前订购材料。
❓ 常见问题
输入您的项目尺寸，即可获得材料数量和成本估算。
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✅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.