Server Rack Power & Cooling Calculator

Totals the power of every device in a rack, shows amps per phase, how many circuits the 80% continuous rule requires, heat in BTU/h and tons of cooling, and a yearly electricity cost with PUE applied.

For IT staff and small server room owners.

Last updatedHow we build & check our tools
Results will appear here once you enter your values.

How the calculation works

Single-phase current is watts divided by volts. Three-phase current per line is watts divided by volts times the square root of 3, using line-to-line voltage and a balanced load. Supply options are 120, 208 or 240 V.

Default rack: ten 1U servers at 350 W each at 208 V single phase on a 30 A breaker, PUE 1.5 and $0.12 per kWh. Total load is 3,500 W, or 16.83 A. One circuit is enough, because 16.83 A is under the 24 A usable limit. Heat is 11,942 BTU/h, or 0.99 tons. Annual energy is 3.5 kW x 8,760 h x 1.5 = 45,990 kWh, which costs $5,518.80.

  • Rows: up to 100 devices, each with a name, a power or current, and a quantity.
  • Breaker: any rating above 0 A and up to 1,000 A.
  • Rate: $0 to $100 per kWh.

What this tool is not

This is a planning estimate and not an electrical or data center design. It does not check wire size, PDU ratings, phase balance, power factor, inrush, or redundancy. A rack with dual-feed servers needs to be designed so that one feed alone can carry the load.

  • Electrician: have a licensed electrician confirm circuits, breakers and receptacles.
  • Cooling: airflow, containment and hot spots matter as much as total tons.
  • Local code: your jurisdiction may adopt a different NEC edition.

Sources and next steps

NFPA 70, National Electrical Code, Sections 210.20(A) and 215.3 (continuous loads at 80% of the overcurrent device rating). The Green Grid, 'PUE: A Comprehensive Examination of the Metric' (2012) for the definition of power usage effectiveness. Conversion constants: 1 W = 3.412 BTU/h and 12,000 BTU/h = 1 ton of cooling.

To work out the cost of any single appliance, use the kWh cost calculator. For three-phase math, use the three-phase calculator, and for UPS runtime try the battery runtime calculator.

Frequently Asked Questions

Common questions about the Server Rack Power & Cooling Calculator

The tool derates each breaker to 80% of its rating for continuous load, following NEC 210.20(A) and 215.3, then divides total rack amps by that usable amps. A 30 A breaker gives 24 A usable. At 208 V single phase that is 4,992 W per circuit. The answer is rounded up, and it assumes one circuit per PDU with no A and B redundancy.

Sources & References

International System of Units (SI): energy, work and heat

Energy, work and heat is measured in the joule (J); 1 cal = 4.184 J. Conversions between SI and other units use exact, internationally agreed factors maintained by NIST.
→Source: NIST — International System of Units (SI)

International System of Units (SI)

Authoritative definitions for energy, work and heat, from the BIPM SI Brochure (9th edition), the defining reference for the SI.
→Source: BIPM — SI Brochure (9th ed.)

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