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Calcimator

Rack Power Density Calculator

Calculate per-rack power density, circuit sizing, and cooling requirements from server count and power draw.

Inputs

Results

Total rack power (kW)

7.4

Density class (1-4)2
Watts per U176.2
U-space utilization (%)52.4%
Circuit current (A)35.6
Recommended breaker (A)50
Circuits needed1
Heat output (BTU/hr)25,249
How to Use This Calculator
  1. Enter the number of servers per rack and power draw per server.
  2. Set PDU redundancy (A+B feeds) and UPS design margin.
  3. Review kW per rack, required PDU amperage, and circuit breaker size.
  4. Flag racks exceeding 10 kW/rack for supplemental cooling (in-row or rear-door).
  5. Use the amperage output to specify PDU ratings and branch circuit protection.

How the result changes with Servers per rack

Servers per rackTotal rack power (kW)
103.9
3512.65
6523.15
9031.9

What each input means

Servers per rack
Number of servers installed in this rack.
Watts per server
Average power draw per server. 1U: 300-500W, 2U: 500-1000W, GPU: 1500-4500W.
Switches per rack
Number of network switches (ToR) in the rack.
Watts per switch
Power draw per network switch. 1G: 50-100W, 10G: 150-300W, 100G: 300-500W.
Other equipment (W)
Power for PDU overhead, monitoring, cable management lighting, etc.
Rack height (U)
Total rack units available. Standard: 42U, also common: 45U, 48U.
Server height (U)
Height of each server in rack units (1U, 2U, 4U, etc.).
Circuit voltage (V)
Power circuit voltage. Common: 120V, 208V (single-phase), 415V (3-phase).

What each result means

Total rack power (kW)
Total power draw of the rack in kilowatts.
Density class (1-4)
1=Low (<5kW), 2=Medium (5-10kW), 3=High (10-20kW), 4=Ultra-high (20+kW).
Watts per U
Average power per rack unit of cabinet height.
U-space utilization (%)
Percentage of rack units occupied by equipment.
Circuit current (A)
Amperage required at the specified voltage.
Recommended breaker (A)
Breaker size per NEC 80% continuous load rule.
Circuits needed
Number of power circuits required for this rack.
Heat output (BTU/hr)
Heat rejected by the rack in BTU per hour.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Servers per rack = 20, Watts per server = 350, Switches per rack = 2, Watts per switch = 150 = 8 input(s) provided
  2. Calculate Total rack power
    Total rack power = totalRackW / 1000
    7.4 = 7.4
  3. Calculate Density class
    2 = 2
  4. Calculate Watts per U
    176.2 = 176.2

Engine last updated .

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