Planner · Homelab & IT
Server rack planner that checks the power, heat and weight too
Lay out a 19-inch rack device by device and see, as you type, whether the cabinet still fits, whether the circuit holds, how much heat you have to move, and what size UPS keeps it alive. Nothing is sent anywhere.
Rack and supply
inputsAdd equipment
presetsCustom device
Blank and spacer rows are real devices with 0 W — they keep gaps in the elevation honest.
Rack elevation
U1 at the bottomDevice detail
nameplate| U | Device | Cat | U | W | kg | mm |
|---|
What to fix before you buy
How the numbers are worked out
Every figure below is arithmetic you can check by hand. No algorithms are hidden and nothing is fetched from a server.
Space
One rack unit is 44.45 mm (1.75 in). Used space is the sum of device heights; free space is the rack height minus that sum. A device that does not fit is refused rather than silently overflowing.
Power and circuit
Current equals watts divided by volts.
Continuous loads are limited to 80% of the
breaker rating, so the planner compares draw
against breaker × 0.8 and
flags anything above it.
Heat and airflow
Drawn power becomes heat: BTU/h = W × 3.412. Airflow to remove it is about 3.16 CFM per watt per °F of accepted rise, which is 2.98 m³/h per watt per °C.
UPS
Apparent power is
W / power factor; the planner
recommends 25% headroom above that. Runtime
assumes 85% inverter efficiency and 60%
usable battery depth.
What this is not: a substitute for a licensed electrician, a thermal survey or a manufacturer's rail-depth check. It is a planning estimate built from nameplate figures. Confirm final loads against real measured draw before committing.
Questions
What is a rack unit (U)?
One rack unit equals 44.45 mm (1.75 inches) of vertical space. A standard full-height rack is 42U; network cabinets are commonly 12U to 24U. Device heights are quoted in whole U so the elevation always adds up exactly.
How much power can a server rack draw from one circuit?
A continuous load must not exceed 80% of the breaker rating. On a 120 V 15 A circuit that is 12 A (~1,440 W); on 120 V 20 A it is 16 A (~1,920 W); on 230 V 16 A it is 12.8 A (~2,944 W). The planner compares your total nameplate draw against the breaker you choose and warns when you cross that line.
How do I calculate the heat load of a rack?
Essentially all electrical power drawn by IT equipment becomes heat: BTU per hour equals watts multiplied by 3.412. The airflow needed to carry that heat away depends on the temperature rise you accept across the equipment, using the standard relationship of about 3.16 CFM per watt per degree Fahrenheit of rise.
What size UPS does a rack need?
Convert real power to apparent power by dividing watts by the power factor (about 0.9 for modern switching supplies), then add 25% headroom so the UPS runs below full load. Runtime is governed by battery capacity, so this planner asks for battery watt-hours and reports an estimated runtime that assumes 85% inverter efficiency and 60% usable battery depth.
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