Rack Cooling
Calculate cooling capacity required to dissipate heat load from a server rack.
About Rack Cooling
Nearly all electrical power consumed by IT equipment is ultimately dissipated as heat (a server doesn't store energy — it converts it to computation and, overwhelmingly, waste heat), so a rack's power draw in watts converts directly to a cooling load using the standard conversion of 3.412 BTU/hr per watt. Cooling capacity is often specified in 'tons of refrigeration' (a legacy unit equal to 12,000 BTU/hr, originally referencing the cooling effect of melting one ton of ice per day), so dividing total BTU/hr by 12,000 gives the tonnage of CRAC/CRAH capacity needed — with a safety margin added to avoid running cooling infrastructure at its absolute limit.
Formulas
Heat load
BTU_hr = watts × 3.412
Tons of cooling
tons = BTU_hr / 12000
Worked example
With the default values below, Rack Cooling returns Recommended Cooling Capacity (with margin) of 1.63. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Total Rack Power Drawminimum 0 W
- 5,000 W
- Safety Marginaccepts 0–50
- 15
Results
- Recommended Cooling Capacity (with margin)
- 1.63 tons
- Heat Load
- 17,060 BTU/hr
- Cooling Required (no margin)
- 1.42 tons
- Recommended Heat Load Capacity (with margin)
- 19,619 BTU/hr
Step by step
- 1Values used
- 2Heat load
- 3Tons of cooling
- 4Recommended Cooling Capacity (with margin)= 1.63 tons
- 5Heat Load= 17,060 BTU/hr
- 6Cooling Required (no margin)= 1.42 tons
- 7Recommended Heat Load Capacity (with margin)= 19,619 BTU/hr
Assumptions and limits
- The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why does IT power draw equal cooling load?
By the first law of thermodynamics, energy can't be destroyed — the electrical power consumed by servers, storage, and networking gear is converted into computation (a negligible fraction) and, almost entirely, waste heat radiated into the room, so the cooling system must remove heat at essentially the same rate the IT equipment consumes power.
Where does the 3.412 BTU/hr per watt conversion factor come from?
It's the standard energy unit conversion: 1 watt = 1 joule/second, and 1 BTU = 1055.06 joules, so 1 watt sustained for one hour equals 3600 joules = 3600/1055.06 ≈ 3.412 BTU — this is a fixed physical conversion, not an approximation specific to data centers.
Why add a safety margin on top of the calculated cooling load?
Running cooling infrastructure at exactly its rated capacity leaves no margin for equipment additions, higher ambient temperatures, partial CRAC/CRAH unit failures, or airflow inefficiencies (hot spots, bypass air) — a 15-20% margin is a common planning buffer to maintain safe operating temperatures under real-world, non-ideal conditions.