Colocation Rack Power Calculator
List the equipment going into your rack to estimate total power, current draw, heat output, and the number of U you need.
| Device | Quantity | U per unit | Watts per unit |
|---|
Default wattages are rough averages and can be edited. Set the voltage to match your facility (230 V in most of Europe, Asia and Africa; 120/208 V in North America). For accurate results, use actual draw from iDRAC/iLO/IPMI or a PDU.
Free, no sign-up. Everything runs in your browser.
How to calculate rack power requirements
- Total watts = sum of (watts per unit × number of units).
- Amps = watts ÷ (voltage × power factor). At 220 V and PF 0.9, every 1,000 W draws about 5 A; at 120 V it is about 9.3 A.
- kVA = watts ÷ power factor ÷ 1,000, used to choose UPS and circuit capacity.
- Recommended circuit = amps ÷ 0.8, following the 80% maximum load rule.
- Heat = watts × 3.412 BTU/hr.
Colocation planning tips
- Use dual PSUs and two power feeds (A+B) for production servers, so one circuit can fail without taking equipment down.
- Measure your servers' actual draw over a few days before you move. PSU label ratings are almost always too high.
- Leave a few spare U and about 20% power headroom for growth.
- Note your uplink needs: number of ports, speed (1G/10G), and whether you need public IPs or a BGP session.
Frequently asked questions
How do I find out how much power my server uses?
The most accurate way is to measure actual draw through iDRAC, iLO, IPMI, or a metered PDU. The wattage on the power supply (PSU) label is its maximum capacity, not everyday usage; servers typically draw 30–60% of that figure.
What is the difference between watts, amps, and kVA?
Watts are the real power a device consumes. Amps are the electrical current at a given voltage (230 V in most of Europe, Asia and Africa; 120/208 V in North America). kVA is apparent power, watts divided by the power factor, and is used to size UPS units and electrical circuits.
What is the 80% rule for rack circuits?
Common data center practice is to keep continuous load at no more than 80% of the breaker rating. For example, a 16 A circuit should carry at most about 12.8 A, leaving headroom for inrush when equipment powers on so the breaker does not trip.
How many U are in a full rack?
A standard 19-inch data center rack is usually 42U; 45U and 47U racks also exist. One U equals 1.75 inches (44.45 mm) of vertical space. Besides equipment, leave room for patch panels, cable management, and PDUs.
Why calculate heat (BTU/hr)?
Almost all the electrical power a device uses turns into heat. The BTU/hr figure helps estimate cooling requirements; 1 watt produces about 3.412 BTU/hr.
Ready to colocate your servers?
Send these results to the Cloudku sales team. We will prepare a quote for rack space, power, and connectivity at our colocation facility in Surabaya, Indonesia.