Power Load Inputs
Enter wattage first. Current is used only when watts are blank.
Example Data Table
| Load | Watts Per Unit | Quantity | Demand Factor | Demand Watts |
|---|---|---|---|---|
| LED lighting | 18 W | 20 | 100% | 360 W |
| Exhaust fan | 180 W | 2 | 80% | 288 W |
| Portable tools | 1,200 W | 2 | 60% | 1,440 W |
| Total demand | 2,088 W |
Formula Used
Rated watt input: Load watts = watts per unit × quantity.
Current input: Single-phase AC watts = voltage × current × power factor. Three-phase AC watts = √3 × voltage × current × power factor. DC watts = voltage × current.
Demand load: Demand watts = Σ(load watts × demand factor ÷ 100).
Design load: Design watts = demand watts × (1 + safety margin ÷ 100).
Estimated current: Single-phase AC current = design watts ÷ (voltage × power factor). Three-phase AC current = design watts ÷ (√3 × voltage × power factor). DC current = design watts ÷ voltage.
Breaker estimate: Required breaker current = estimated current ÷ utilization limit. The calculator rounds upward to the next listed standard size.
How to Use This Calculator
- Select the correct system type and enter supply voltage.
- Enter power factor for AC loads. Use 1.00 for DC.
- Add each load with watts or current, quantity, and demand factor.
- Choose a safety margin and breaker utilization limit.
- Press Calculate Total Load to review power, current, energy, and breaker guidance.
- Compare the result with equipment data, conductor limits, and local requirements.
Planning a Reliable Circuit
Start With Complete Load Data
Power load planning starts with a complete equipment list. Record every fixed appliance, motor, heater, lighting group, receptacle allowance, and electronic device. Enter the rated watts when nameplate data is available. Use rated current when wattage is missing. The calculator changes current into estimated watts using the selected voltage, system type, and power factor. Quantity matters. Ten small fixtures can create more demand than one large tool. Separate loads also make later review easier.
Label each entry with its location or purpose. This prevents duplicate entries and reveals circuits that may be heavily used at the same time. Include spare outlets only when the design brief requires them for expansion.
Apply Demand Realistically
Connected load is not always the same as operating demand. Some equipment runs only occasionally. Other equipment starts together during busy periods. A realistic demand factor helps estimate normal use without ignoring important capacity. Use conservative values when the project schedule or equipment behavior is uncertain. A safety margin then increases the calculated demand. This supports future additions, measurement variation, and practical design flexibility. Do not use an aggressive diversity assumption to force a smaller circuit.
Account for Electrical Conditions
Power factor affects alternating-current equipment. Resistance heaters and incandescent lamps commonly operate near unity power factor. Motors, drivers, transformers, and some electronic supplies may operate lower. A lower power factor raises current for the same useful watt demand. For a three-phase circuit, line current also depends on the square root of three. Select the correct system setting before relying on the current result. Confirm voltage at the actual supply point.
Review Protection and Records
Breaker selection needs more than total watts. Compare calculated current with the intended breaker rating and the chosen continuous-use limit. Long operating periods may require additional allowance. Conductor size also depends on insulation rating, installation method, ambient temperature, number of current-carrying conductors, voltage drop, and local rules. This page gives a planning estimate. It does not replace drawings, measurements, or a qualified electrical design review.
Use the result table to identify the largest contributors. Reduce unnecessary connected equipment where possible. Move large loads to separate circuits when operation overlaps. Check motor starting requirements separately because starting current can exceed running current. Recalculate after equipment changes. Keep a copy of the final load schedule with panel records. Clear records make future maintenance and expansion safer.
Frequently Asked Questions
What is total power load?
Total power load is the combined electrical demand of connected equipment. It can include rated watts, calculated watts from current, demand factors, and a selected safety margin.
Can I enter current instead of watts?
Yes. Leave watts blank and enter amps per unit. The calculator estimates watts from voltage, selected system type, and power factor.
Does system type change the result?
Yes. Three-phase calculations use the square root of three. DC calculations do not use power factor. Select the supply arrangement that matches the circuit.
Why does power factor matter?
AC equipment with lower power factor draws more current for the same real power. This can change the estimated current and breaker guidance.
What demand factor should I use?
Use a value that reflects how often each load operates at the same time. When uncertain, use a conservative value and confirm local design requirements.
Why add a safety margin?
A safety margin allows for future equipment, measurement uncertainty, and practical operating variation. It does not replace required engineering or installation checks.
Does the suggested breaker size approve my circuit?
No. It is a planning estimate. Final protection must suit conductors, installation conditions, equipment instructions, and applicable rules.
Can this calculator handle three-phase circuits?
Yes. Choose Three-phase AC. The calculation applies the square root of three to derive watts from current and to estimate line current.
What is the difference between watts and VA?
Watts represent real power. VA represents apparent power. On AC systems, VA is higher than watts when power factor is below one.
Should motor starting current be included?
Consider motor starting current separately. This calculator estimates running demand. Motor starting, inrush, and protective-device behavior need equipment-specific review.
Is this calculator a code approval tool?
No. Use it for planning. Verify the design against applicable codes, equipment instructions, and a qualified professional. Check local requirements before finalizing any circuit design decisions.