Electric Load Calculator (Single-Phase & Three-Phase)
Estimate connected load, running current, daily energy use, and a recommended breaker size. Add up to 4 appliance groups.
Appliance Loads
Use less than 100% if all connected loads do not run simultaneously.
What Is an Electric Load Calculator?
An electric load calculator helps you estimate how much power your home, office, or workshop will draw based on connected appliances. Instead of guessing, you can calculate total watts, current in amps, daily energy in kWh, and a practical breaker target. This is useful for planning circuits, checking panel capacity, sizing backup power systems, and reducing nuisance breaker trips.
In simple terms, load calculation translates your equipment list into numbers that matter for electrical design and safety.
Why Load Calculation Matters
- Safety: Prevent overloaded circuits and overheating conductors.
- Cost control: Estimate monthly energy use and utility impact.
- System reliability: Choose better breaker and wire sizes.
- Project planning: Determine whether your service panel can support new loads like EV chargers or HVAC upgrades.
Core Inputs Explained
1) Watts (W)
Watts represent real power consumed by a device. Most appliances show wattage on the nameplate or manual. For motor-driven equipment, starting current can be much higher than running power, so account for that when selecting protection devices.
2) Quantity
If you have multiple identical devices (for example, 12 downlights or 4 fans), multiply watts by quantity to get connected load for that group.
3) Voltage
Common values are 120V or 230V for single-phase and 400V or 415V line-to-line for many three-phase systems. Current depends strongly on voltage: for the same power, higher voltage means lower current.
4) Power Factor (PF)
Power factor links real power to apparent power. Resistive loads are close to 1.0. Motors and compressors can be lower. A realistic PF improves current estimation accuracy, especially for larger systems.
5) Demand Factor
Demand factor reflects diversity. Not all connected appliances run at full power at the same time. For planning, many installations use less than 100%, depending on load type and usage behavior.
Formulas Used by This Calculator
| Output | Formula |
|---|---|
| Connected Load (W) | Sum of (Watts × Quantity) for all appliance groups |
| Demand Load (W) | Connected Load × (Demand Factor / 100) |
| Current, Single-Phase (A) | I = P / (V × PF) |
| Current, Three-Phase (A) | I = P / (√3 × V × PF) |
| Daily Energy (kWh) | (Demand Load × Hours per Day) / 1000 |
| Recommended Breaker Target (A) | Current × 1.25 (then choose next standard breaker rating) |
How to Use the Calculator Effectively
- Enter your supply type and voltage.
- Add realistic watts and quantities for major appliances.
- Set power factor (0.9 to 1.0 for many mixed loads, unless you have better data).
- Apply demand factor if loads are not simultaneous.
- Review computed current and breaker recommendation.
Practical Tips for Better Accuracy
- Use nameplate running watts where possible.
- Separate continuous loads (3+ hours) and size circuits conservatively.
- For motors and compressors, account for startup surge and manufacturer breaker guidance.
- Recalculate after adding major equipment such as water heaters, ovens, or EV chargers.
Breaker and Cable Sizing: Quick Guidance
The calculator suggests a breaker by applying a 125% margin and then rounding to a standard rating. In real design work, breaker coordination and cable ampacity must match local standards, insulation type, installation method, ambient temperature, and grouping factors.
Use this page as a pre-design estimate, then verify with your local codebook and a qualified electrician.
Frequently Asked Questions
Is connected load the same as billable energy?
No. Connected load is installed capacity. Billable energy depends on how long loads run (kWh).
What demand factor should I choose?
It depends on usage. Homes might use lower demand factors than workshops with simultaneous machinery. Start with 70% to 100% and compare scenarios.
Why include power factor?
Because current is influenced by PF. Ignoring PF can under- or overestimate amp draw, especially on inductive loads.
Final Thoughts
An electric load calculator is one of the simplest ways to improve electrical planning decisions. With accurate inputs, you can better estimate amp demand, choose sensible protection, and get a clearer view of expected energy consumption before you install new loads.