Data Center Power Calculator
Estimate a rack's power load: total kilowatts from your device mix, current against the circuit's 80% continuous-load limit, and what that load costs per month.
Total load
6.50 kW
Current
28.3 A
80% limit
25.6 A
Monthly cost
$702
Amps = watts ÷ volts. Monthly kWh here assumes constant draw (4680 kWh); real loads vary — measured per-device data beats estimates.
Rack Circuit Capacity: kVA and kW From Volts, Amps and Phase
The calculator above works out what your equipment draws. This one works out what the rack's feeds can actually deliver — the number that decides how much you are allowed to install.
Per feed
7.36
kVA
Usable capacity
7.36
kVA · 6.99 kW
Derated (80%)
5.59
kW continuous — plan to this
Headroom vs load above
-0.91
kW
Single-phase kVA = volts × amps ÷ 1000. Three-phase multiplies by √3 (1.732). kW = kVA × power factor — modern PFC server supplies sit around 0.95–0.99.
Nameplate Watts Lie. Measured Watts Don't.
Calculators plan; meters know. PSU nameplate ratings can overstate real draw by 2–3×, so racks planned on nameplate run half-empty while the circuit still has headroom. Reading actual per-server draw from the BMC and per-outlet data from intelligent PDUs turns this estimate into a measurement — and usually finds capacity you didn't know you had.
Power Planning Questions
How do you calculate rack power consumption?
Sum the real draw of every device in the rack (servers × watts each, plus network and storage gear). Convert to current with amps = watts ÷ volts, and keep total load within 80% of the circuit's breaker rating for continuous loads.
What is the 80% rule for circuits?
Electrical codes derate circuits for continuous load: a 30A circuit should carry at most 24A continuously. Rack power planning that ignores the 80% rule trips breakers under peak load.
How much power does a server use?
A typical 1U/2U server draws 150–400W under normal load; dense GPU servers can draw 2–10kW each. Nameplate PSU ratings overstate real draw significantly — measured data from the BMC or PDU is far more accurate for planning.
How do you convert kVA to kW?
kW = kVA × power factor. Modern server power supplies are active power factor corrected and typically run at 0.95–0.99, so a 280 kVA rack feed is roughly 266–277 kW of usable real power. Use 1.0 only if the equipment is genuinely unity power factor.
How many kVA does a rack circuit provide?
For a single-phase circuit, kVA = volts × amps ÷ 1000. A 230V 32A circuit is 7.36 kVA. For three-phase, multiply by √3 (1.732): a 400V 32A three-phase circuit is 22.2 kVA. Derate to 80% for continuous load before treating any of it as usable.
How many amps does a 550W server power supply draw?
Amps = watts ÷ volts, so a server actually drawing 550W pulls about 2.4A at 230V or 4.6A at 120V. Note that 550W is usually the PSU's nameplate rating, not its real consumption — measured draw is typically well below it.
What does A/B redundant power mean for rack capacity?
With dual A/B feeds, each feed must be able to carry the entire rack alone so the rack survives losing one. Usable capacity is therefore the capacity of a single feed, not the two added together — two 32A feeds give you one 32A feed's worth of load, with the second as spare.