Rack power, PUE and UPS runtime calculator
How much do your servers draw, and how much does everything around them cost? Three calculations: the power, cost and heat of a set of servers, a room's PUE, and a UPS's runtime. The formulas are under the result.
The calculation runs in your browser: nothing you type is sent anywhere.
Power, consumption and heat
Result
Yearly electricity cost
6,570 € excl. VAT
3,285 € excl. VAT for the machines, 3,285 € excl. VAT for cooling and losses
IT load
1.50 kW
i.e. 1.53 kVA (power factor 0.98)
Energy per year
26,280 kWh
of which 13,140 kWh for IT
Heat to remove
5,118 BTU/h
i.e. 1.50 kW of cooling
Matching colocation allowance
Half rack: the load fits within about 2 kVA contracted.
300 W per U on average
PUE calculation
Result
PUE
2.00
50% of the energy does not reach IT
UPS runtime
Result
Estimated runtime
31 min
156 Wh of usable energy
How the calculation works
IT power is the sum of the average draws actually measured, not the power supply rating on the label. Everything else follows:
P (kW) = servers × average W + other equipment
S (kVA) = P / cos φ (cos φ ≈ 0.98)
E_IT (kWh/yr) = P × 8,760 h
E_total = E_IT × PUE
yearly cost = E_total × price per kWh
heat = P × 3.412 BTU/h per wattPUE (Power Usage Effectiveness) relates the facility's total energy to the energy of the IT equipment alone. Its definition is standardised in ISO/IEC 30134-2. A PUE of 2 means one kWh of IT costs two at the meter: the second goes to air conditioning, UPS units, conversion losses and lighting. A small room rarely gets below a PUE of 2. Datacenters publish their own figure: check the period and measurement point it is based on before comparing.
UPS runtime is estimated from the usable energy of its batteries:
usable energy (Wh) = V × Ah × strings × depth of discharge × efficiency
runtime (min) = usable energy / load (W) × 60What the calculation says about your room
By default the calculator uses the example from our comparison server room or datacenter: five 300 W servers, 0.25 € excl. VAT per kWh, a PUE of 2. Powering the machines costs 3,285 € excl. VAT a year, and about the same again for cooling and losses, roughly 6,600 € excl. VAT a year. That figure is accurate, but it is only the visible part: the page details air conditioning servicing, UPS testing, the generator and on-call cover, which weigh more than the kWh.
The colocation allowance shown under the result follows the market practice described in that comparison: per U, pricing assumes 100 to 150 W per U; beyond 3 to 4 U, a quarter rack with about 1 kVA contracted becomes the better deal, then a half rack with about 2 kVA. Above that, contracted power decides, not the number of U. Our own racks are at Equinix, in the Paris region: the list of Equinix datacenters where we are present (fr) is published with our network.
A UPS covers a short outage, from a few minutes to half an hour depending on its sizing. It replaces neither the generator nor cooling: when air conditioning stops, the temperature rises within minutes, UPS or not. We lived through it and documented it during the cooling incident at Equinix PA4.
After the calculation
UPS runtime only matters if someone is alerted when it switches to battery, at night or at the weekend. That is the job of 24/7 IT on-call support, which also monitors temperature and redundant power supplies.
And a power outage always ends up as minutes of downtime. To see how many your service commitment allows, and what a redundant power feed gains you, go to the uptime and SLA calculator.
Frequently asked questions
How do you calculate PUE?
Divide the total energy used by the facility by the energy used by the IT equipment alone, over the same period. A room drawing 26,280 kWh a year at the main meter for 13,140 kWh measured at the UPS output has a PUE of 2: half the energy goes to cooling and losses. A PUE of 1 would be a room with no overhead at all.
How much does a 300 W server cost in electricity per year?
300 W drawn continuously is 2,628 kWh a year, or 657 € excl. VAT at 0.25 € excl. VAT per kWh. In a small room, which rarely gets below a PUE of 2, budget the same again for cooling and losses: 1,314 € excl. VAT a year per server.
What is the difference between kW and kVA for a rack?
kW is the power actually consumed, kVA the apparent power the supplier must deliver. The power factor links the two. IT power supplies with active correction sit around 0.98: five 300 W servers draw 1.5 kW, or 1.53 kVA. The two values are almost the same.
How long will a UPS last?
As a first approximation: battery bank voltage × capacity × depth of discharge × efficiency, divided by the load. Two 12 V 9 Ah batteries in series (24 V), discharged to 80% with 90% efficiency, give 155.5 Wh of usable energy, about 31 minutes at 300 W. Under heavy load, real runtime is shorter (Peukert's law): the manufacturer's curves prevail.
How many BTU/h must a server room remove?
All the energy IT consumes ends up as heat. 1 W equals 3.412 BTU/h: 1.5 kW of IT gives off about 5,118 BTU/h, i.e. 1.5 kW of cooling, plus lighting, people and outside heat gains.
Contact
Address
5 B RUE DES NOYERS, 95300 PONTOISE, FRANCE