Server Rack Power Cost Calculator

Related Calculators

Table of contents

• How to use
• Common mistakes
• Definitions
• Methodology
• Limitations & assumptions
• Sources

Average IT load: The total server equipment power in kilowatts before facility overhead is added.

kWh: Kilowatt-hour, the energy unit used for many electric bills. A 1 kW load running for 1 hour uses 1 kWh [3].

PUE facility multiplier: Power usage effectiveness. It compares total facility energy with IT equipment energy. A PUE of 1.50 means the facility uses 1.5 kWh for each 1 kWh used by the rack equipment.

IT-only monthly power cost: The monthly energy cost from server equipment only, before PUE is applied.

Facility-adjusted monthly power cost: The main estimate after multiplying IT energy by the PUE facility multiplier and the Electricity price.

Power factor: A ratio from above 0 to 1 that connects real power in watts with electrical current in amps.

Continuous-load limit: The percent of circuit rating used for a continuous load planning check.

Cooling ton: A cooling capacity unit equal to 12,000 BTU/h, used here to estimate cooling needed for rack heat.

Mistake: Using a monthly bill total in Electricity price.
Fix: Enter the price per kWh, such as 0.15, so Facility-adjusted monthly power cost is based on energy price.

Mistake: Entering nameplate watts for Average power per server when the servers usually draw much less.
Fix: Use measured average watts if available, or treat the result as a high estimate.

Mistake: Leaving Run time at 24 when the rack is not always on.
Fix: Enter the real hours per day so Facility-adjusted energy use per month matches the schedule.

Mistake: Using a PUE facility multiplier below 1.00.
Fix: Enter 1.00 for no facility overhead, or a value above 1.00 when cooling and support energy should be included.

Mistake: Comparing Estimated rack feed current only with the breaker label.
Fix: Use Minimum circuit rating before rounding with the Continuous-load limit to check the continuous load plan.

Mistake: Choosing the wrong Rack feed phase or Rack feed voltage.
Fix: Match the actual rack feed, because single-phase and three-phase current are calculated differently.

• The calculator assumes each server uses the same Average power per server. Mixed servers, storage shelves, switches, and PDUs are not itemized separately.
• Facility-adjusted monthly power cost uses the entered Electricity price only. Real bills can also include demand charges, taxes, minimum fees, time-of-use pricing, or separate delivery charges.
• The yearly result is 12 times the selected monthly pattern. It does not model different month lengths, seasonal rates, or changing workloads.
• PUE facility multiplier is user-entered. If your data center or colocation provider gives a different billing method, that billing method may not match a simple PUE multiplier.
• Estimated rack feed current uses Average IT load, Rack feed voltage, Rack feed phase, and Power factor. It is a planning estimate, not an electrical design approval.
• Minimum circuit rating before rounding is shown before selecting a standard breaker size. Local code, equipment listing, redundancy rules, and electrician review can require a different circuit plan.
• Heat from the rack equipment assumes server electrical power becomes heat in the room. Actual cooling design can also depend on airflow, room layout, return-air temperature, and redundancy needs.

Calculation steps

The calculator first turns the server count and average server watts into Average IT load.

it_load_kw = Number of servers * Average power per server / 1000

It then calculates the monthly run hours from the schedule.

monthly_hours = Run time * Run days

IT-only energy is the rack equipment energy before facility overhead.

it_monthly_kwh = it_load_kw * monthly_hours

Facility-adjusted energy applies the PUE facility multiplier.

facility_monthly_kwh = it_load_kw * PUE facility multiplier * monthly_hours

Cost uses the entered Electricity price in dollars per kWh. Electricity bills commonly measure energy in kWh [3].

facility_monthly_cost = facility_monthly_kwh * Electricity price

annual_facility_cost = facility_monthly_cost * 12

it_monthly_cost = it_monthly_kwh * Electricity price

pue_overhead_monthly_cost = facility_monthly_cost - it_monthly_cost

Heat and cooling are estimated from the IT equipment load.

heat_btu_per_hour = it_load_kw * 1000 * 3.412141633

cooling_tons = heat_btu_per_hour / 12000

Rack feed current uses the IT load, not the PUE-adjusted facility load. For single-phase power, the calculator uses voltage times power factor. For three-phase power, it also divides by the square root of 3.

single_phase_amps = it_load_kw * 1000 / (Rack feed voltage * Power factor)

three_phase_amps = it_load_kw * 1000 / (1.7320508075688772 * Rack feed voltage * Power factor)

minimum_circuit_rating_amps = estimated_line_amps / (Continuous-load limit / 100)

Mini-example

For 10 servers at 300 W each, Average IT load is 10 * 300 / 1000 = 3.00 kW. Running 24 hours per day for 30 days gives 720 hours. With a PUE facility multiplier of 1.50, facility energy is 3.00 * 1.50 * 720 = 3,240 kWh. At $0.15 per kWh, Facility-adjusted monthly power cost is 3,240 * 0.15 = $486.00, and Facility-adjusted yearly power cost is $5,832.00.

Validation and edge cases

Number of servers must be at least 1 and must be a whole number. Average power per server must be above 0 W. Electricity price must be 0 or higher. Run time can be 0 to 24 hours per day, and Run days can be 0 to 31 days per month. If Run time or Run days is 0, energy and cost are 0, but Estimated rack feed current still uses the server load. PUE facility multiplier must be 1.00 or higher. Power factor must be above 0 and no more than 1.00. Continuous-load limit must be above 0 and no more than 100 percent.