Example 1: Small residential feeder
Lighting = 800 W, socket load = 1200 W, HVAC = 2500 W, other = 300 W.
Connected load = 4800 W
Demand load at 80% = 3840 W
At 230 V and PF 1.0, current = 3840 / 230 = 16.70 A
Load Calculation Calculator
Use this online load calculation calculator to total connected load, apply demand factor, and estimate feeder or service current for single-phase and three-phase systems.
Introduction
A load calculation calculator helps you estimate how much electrical demand a feeder, distribution board, or service may need to carry. Instead of assuming every connected load runs at full output at the same time, a demand factor is often applied to estimate the likely maximum demand more realistically.
This electrical load calculation calculator is useful for homes, offices, workshops, and small commercial systems. It helps you estimate connected load, demand load, and current so you can plan feeders, panelboards, breakers, and cable sizes with more confidence.
It also gives a clearer starting point for distribution planning by turning a mixed set of loads into a more realistic demand figure for electrical design decisions.
Formula
Connected load: Pconnected = sum of all load categories
Demand load: Pdemand = Pconnected x Demand factor
Single phase current: I = Pdemand / (V x PF)
Three phase current: I = Pdemand / (sqrt(3) x V x PF)
Demand load: Pdemand = Pconnected x Demand factor
Single phase current: I = Pdemand / (V x PF)
Three phase current: I = Pdemand / (sqrt(3) x V x PF)
Variable Definitions
| Variable | Meaning | Typical Unit |
|---|---|---|
| Pconnected | Total connected load before diversity | W or kW |
| Pdemand | Estimated maximum demand after demand factor | W or kW |
| Demand factor | Expected proportion of connected load operating together | % |
| PF | Power factor | Unitless |
| I | Estimated feeder current | A |
Units
Enter all category loads in watts, demand factor as a percentage, supply voltage in volts, and power factor as a decimal from 0 to 1.
Results are displayed in kilowatts and amperes, making the output easier to use when selecting electrical distribution equipment.
Worked Examples
Example 2: Small workshop board
Lighting = 1500 W, socket load = 2000 W, motors = 6000 W, HVAC = 3000 W, other = 1000 W.
Connected load = 13500 W
Demand load at 75% = 10125 W
At 400 V three-phase and PF 0.9, current = 10125 / (sqrt(3) x 400 x 0.9) = 16.24 A
Practical Load Calculation Notes
A good electrical load estimate helps prevent both undersizing and oversizing. If the design current is too low, feeders, breakers, and panels may be overloaded in service. If it is too high, the installation can become more expensive than necessary. This load calculation calculator is best used as an early design tool before final circuit schedules, diversity assumptions, and code-based demand rules are confirmed for the actual building or facility.