Tool
PDU and power capacity calculator
A PDU capacity check compares planned equipment load against a circuit or PDU rating with headroom. It converts total watts to current draw for single or three phase supplies, applies a continuous-load derating where local regulations require it, and reports utilisation against the usable amps.
Enter your own figures below. Everything is calculated in your browser from what you type.
Your load
Supply
Follow local electrical regulations.
Devices
Use nameplate watts for worst case, or measured watts for typical draw.
Utilisation
! WARN86%
3,000 W total, 13.7 A draw, 16.0 A usable.
- Total load
- 3,000 W
- Current draw
- 13.7 A
- Usable amps
- 16.0 A
- Headroom
- 496 W
How this is worked out
Every assumption is on this page and every input is yours to change. A calculator with a hidden coefficient is a persuasion device rather than a tool.
Current is total watts divided by voltage times power factor for single phase, or by root three times line voltage times power factor for three phase with a balanced load. Usable amps are the breaker rating times 0.8 where continuous-load derating applies.
With A and B feeds, the full load is compared against one feed, because each feed must carry everything if the other fails.
Questions about power capacity
What is the 80 percent derating rule?
North American electrical code requires continuous loads to use no more than 80 percent of a breaker rating. The calculator applies this automatically for North American voltages. Always follow local electrical regulations.
What is power factor?
Power factor is the ratio of real power to apparent power, from 0 to 1. Most IT equipment has a power factor of 0.9 to 1.0. Lower power factor means higher current for the same watts.
How do A and B feeds work?
With redundant A and B feeds, each feed must carry 100 percent of the load if the other fails. The calculator compares the full load against one feed and states this clearly in the result.
Nameplate or measured watts?
Nameplate watts are the maximum the device can draw, giving a worst-case calculation. Measured watts are typical draw, giving a realistic figure. Use nameplate for safety, measured for planning.
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