Formula
- Use the units shown beside each field.
- Results update automatically whenever you change an input.
- Displayed values use up to four decimal places, or scientific notation for very small or large numbers. Calculations use standard floating-point arithmetic; exact integer and fraction tools identify their own precision rules.
- Assumes loads start separately while others run. Does not assess kVA, power factor, transient duration, phase imbalance or wiring safety.
Example Calculation
- Running watts of each load: 500,800,1000
- Total starting watts for corresponding loads: 500,1600,3000
- Planning headroom: 20 %
Running loads total 2300 W; largest extra start is 2000 W, so 20% headroom on 4300 W is 5160 W.
Frequently asked questions
How do I use this calculator?
Enter running watts of each load, total starting watts for corresponding loads, planning headroom. The result updates automatically. Use Reset to restore the example values.
What method does it use?
peak=Σrunning + max(starting−running); planned=peak × (1+headroom).. Assumes loads start separately while others run. Does not assess kVA, power factor, transient duration, phase imbalance or wiring safety.
Why might a rounded result differ?
The calculation keeps full numeric precision internally, then rounds the displayed result. Rounding intermediate steps by hand can produce a slightly different answer.
Are my inputs saved online?
No. This calculator processes your inputs in your browser. A recently used list stores only calculator names on this device, not your entered values.
Check the assumptions and units before using this result. Read about calculation methods.