Productive ToolboxElectrical Load Calculator (Building)
Calculate total electrical load for residential and commercial buildings. Estimate kW, current, breaker size, and power usage instantly.
Electrical Load Calculator (Building)
Calculate total electrical load for residential and commercial buildings. Estimate power consumption, current, breaker size, and cable requirements.
Settings
Accounts for not all loads running simultaneously
Appliances & Equipment
| Appliance | Qty | Power (W) | Category | Total | Action |
|---|---|---|---|---|---|
| 0 W |
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About the Electrical Load Calculator
The Electrical Load Calculator (Building) is a professional tool designed for electrical engineers, architects, contractors, and builders to estimate total electrical load for residential and commercial buildings. It calculates power consumption, current requirements, recommended breaker sizes, and cable specifications based on connected appliances and equipment.
⚡Key Features
- •Dynamic appliance table with unlimited rows
- •Pre-built appliance templates for quick entry
- •Real-time load calculation
- •Breaker and cable size recommendations
- •Export to TXT and CSV formats
🎯Use Cases
- •Electrical system design and planning
- •Circuit breaker sizing
- •Cable specification selection
- •Building permit applications
- •Energy consumption estimation
How to Use the Calculator
- 1Set the supply: Choose the voltage (120 V or 240 V in North America, 230 V in the UK, Europe and Australia), the building type and the demand factor.
- 2Add the loads: Enter each appliance with its quantity, power in watts and category, or use the templates.
- 3Adjust the power factor: Leave 0.8–0.9 for typical mixed loads, or 1.0 for purely resistive loads such as heaters.
- 4Read the results: See the connected and demand load in kW, the current, a standard breaker size and a typical copper cable size.
Understanding the Calculations
Step 1: Calculate Total Connected Load
Total Load (W) = Σ (Quantity × Power Rating)Sum the power consumption of all appliances considering their quantities.
Step 2: Apply Demand Factor
Demand Load (kW) = Total Load × Demand FactorApply diversity factor since not all appliances run simultaneously.
Step 3: Calculate Current
Current (A) = (Demand Load × 1000) / (Voltage × Power Factor)Calculate the current draw based on voltage and power factor.
Step 4: Size Breaker
Breaker Size = Current × 1.25 (rounded up to standard size)Add 25% safety margin and round to nearest standard breaker rating.
Example Calculation
Appliances:
• 3 Fans @ 75W = 225W
• 5 Lights @ 15W = 75W
• 1 AC @ 1500W = 1500W
Total: 1800W = 1.8 kW
Demand (80%): 1.44 kW
At 120 V (US): 1440 W ÷ (120 V × 0.8) = 15 A; × 1.25 = 18.75 A → 20 A breaker, 12 AWG
At 230 V (Europe): 1440 W ÷ (230 V × 0.8) = 7.83 A; × 1.25 = 9.78 A → 10 A breaker, 1.5 mm²
Demand Factor Guidelines
100% - No Diversity
All loads running simultaneously (worst case)
90% - Low Diversity
Critical facilities, data centers
80% - Recommended
Typical residential and commercial buildings
70% - High Diversity
Large buildings with varied usage patterns
Standard Breaker Sizes
Common Breaker Ratings (Amps):
Cable Size Reference
| Breaker | Copper cable (metric / US) | Typical use |
|---|---|---|
| 15–16 A | 1.5 mm² (14 AWG) | Lighting circuits |
| 20 A | 2.5 mm² (12 AWG) | General outlets, kitchen circuits (US) |
| 30–32 A | 4–6 mm² (10 AWG) | Water heaters, dryers, cookers, EV chargers |
| 40 A | 6 mm² (8 AWG) | Ranges, larger air conditioners |
| 60–63 A | 16 mm² (6–4 AWG) | Sub-panels |
| 100 A | 35 mm² (3–1 AWG) | Small service or main feeder |
Typical sizes from NEC Table 310.16 and IEC 60364-5-52 for short runs. Long runs, bundled cables, hot locations and local rules can require larger cables; have an electrician confirm the size.
Practical Applications
New Construction
Calculate total electrical load during design phase to properly size main service panel, feeders, and branch circuits.
Renovations
Assess existing capacity and determine if service upgrade is needed when adding new appliances or equipment.
Safety Planning
Prevent circuit overload by ensuring breakers and cables are properly sized for the connected load.
Cost Estimation
Estimate material costs for electrical installation by determining required breaker and cable specifications.
Why Use This Calculator?
- ✓Instant Results: Real-time calculation as you add appliances
- ✓Quick Templates: Pre-built appliance library for fast data entry
- ✓Professional Output: Export detailed reports in TXT or CSV format
- ✓Safety Recommendations: Automatic breaker and cable sizing with safety margins
- ✓Free & Accessible: No registration required
⚠️Important Safety Note
This calculator provides estimates for planning purposes. Always consult with a licensed electrician and follow local electrical codes and regulations. Electrical work should only be performed by qualified professionals. The recommendations provided are general guidelines and may need adjustment based on specific installation conditions, cable routing, ambient temperature, and local code requirements.
Frequently Asked Questions
How do you calculate electrical load?
Add the wattage of everything connected, multiply by a demand factor for the share running at once, then current = watts ÷ (volts × power factor). 1,800 W at 80% demand is 1,440 W; at 120 V and PF 0.8 that is 15 A, and at 230 V 7.8 A.
How is the breaker size chosen?
The current is multiplied by 1.25, as the NEC requires for continuous loads, and rounded up to the next standard rating: 15, 20, 30, 40, 50 A… for 120/240 V, or 6, 10, 16, 20, 25, 32 A… (IEC) for 230 V. 15 A × 1.25 = 18.75 A, so a 20 A breaker.
What demand factor should I use?
100% if everything can run at once, and 70–80% for typical homes and offices, where not every load is on together. The NEC (Article 220) and IEC 60364 give detailed demand factors for dwelling services and feeders.
What is power factor?
The ratio of real power (W) to apparent power (VA). Heaters and incandescent lights are close to 1.0; motors, compressors and some electronics are 0.7–0.9, so they draw more current for the same wattage.
Can I size cables from this?
Only as a first reference. Cable size also depends on run length and voltage drop, how cables are installed and grouped, and ambient temperature, under NEC Table 310.16 or IEC 60364-5-52. A licensed electrician must design and check the installation.
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