Cooling Calculator
BTUs to evacuate for a datacenter or rack based on power consumption.
Heat load (power consumption)
Table of Contents
Comprehensive Datacenter Cooling Guide
What is datacenter cooling?
Datacenter cooling is the set of systems and practices used to remove heat from IT equipment (servers, storage, network gear) and maintain safe temperature and humidity levels. Without adequate cooling, equipment overheats, performance degrades, and failure rates increase. Sizing cooling capacity correctly is essential for reliability, efficiency, and future growth.
Why heat load matters
Virtually all electrical power consumed by IT and support systems is converted into heat inside the room or rack. Lighting, people, and solar gain add a small fraction compared to IT load. The cooling system must remove this heat continuously; otherwise the room temperature rises. The heat load to evacuate is therefore directly tied to total power consumption—hence the rule: power in watts (after applying a safety margin) equals the heat load to size cooling for.
- Heat load: Total heat to remove, in watts or BTU/h. For IT spaces it is essentially equal to total electrical power draw.
- BTU/h: British Thermal Units per hour; common unit for cooling capacity in North America.
- Tons of refrigeration: 1 ton = 12,000 BTU/h. HVAC and CRAC/CRAH units are often specified in tons.
- Safety margin: Extra capacity (e.g. 10–20%%) for peaks, future growth, and redundancy.
Benefits of proper cooling sizing
- Reliability: Equipment stays within manufacturer temperature limits; fewer failures and longer life.
- Efficiency: Right-sized cooling avoids over-provisioning (waste) and under-provisioning (hot spots and risk).
- Planning: Knowing BTU/h or tons helps compare CRAC units, plan redundancy (N+1), and budget.
- Compliance: Many standards (e.g. ASHRAE) recommend temperature and humidity ranges; adequate cooling supports compliance.
Limitations and considerations
- This calculator assumes all electrical power becomes heat in the space. For dedicated IT rooms this is accurate; add lighting and occupancy if in the same zone.
- PDU and UPS losses (typically a few percent) also produce heat inside the room—include them in total power if they are in the cooled space.
- Humidity control (humidification/dehumidification) may require additional capacity; consult HVAC specs.
- Airflow design (hot/cold aisles, containment) affects effectiveness; proper layout improves cooling efficiency.
Undersized cooling leads to hot spots, thermal throttling, and equipment failure. Always use measured or conservative power values and include a safety margin. For critical facilities, consider N+1 or 2N redundancy so cooling continues if a unit fails.
Sizing cooling by power (watts) converted to BTU/h or tons is the standard approach for datacenters and server rooms. Use this calculator to get the required capacity, add a safety margin, and plan for redundancy where uptime is critical. Combine with good airflow design and monitoring for a complete cooling strategy.
Why power equals heat to evacuate
By the first law of thermodynamics, energy is conserved. Electrical power supplied to servers, switches, storage, and PDUs is almost entirely converted into heat: a small part becomes light or sound, but in a datacenter the vast majority ends up as heat in the room. Fans inside equipment move that heat into the room air; the room cooling system (CRAC/CRAH, in-row, or similar) must then remove it.
So for a single rack, a row of racks, or an entire datacenter: add up the power consumption of all IT (and support) equipment in the cooled zone, apply your safety margin, and convert to BTU/h or tons. That is the cooling capacity you need to evacuate. HVAC and CRAC/CRAH units are often specified in tons or BTU/h, which is why this conversion is essential for procurement and design.
BTU and tons of refrigeration
The British Thermal Unit (BTU) is the energy needed to raise the temperature of one pound of water by one degree Fahrenheit. Cooling capacity is usually expressed in BTU per hour (BTU/h): the rate of heat removal. In North America, air conditioning and datacenter cooling are also specified in tons of refrigeration.
1 ton of refrigeration = 12,000 BTU/h. Historically this represented the cooling effect of melting one ton of ice over 24 hours. A 10-ton CRAC unit removes 120,000 BTU/h.
Formulas and conversions
BTU/h = Power (watts) × 3.412
1 watt = 3.412 BTU/h (British Thermal Units per hour). The calculator applies your safety margin to the power before converting.
Tons of refrigeration: 1 ton = 12,000 BTU/h. So Tons = BTU/h ÷ 12,000. Air conditioning and datacenter cooling are often rated in tons (e.g. a 10-ton unit removes 120,000 BTU/h).
Quick reference:
- 1 kW = 3,412 BTU/h ≈ 0.284 tons
- 1 ton ≈ 3.517 kW (heat removal equivalent)
Types of cooling systems
Datacenter and server room cooling can be provided in several ways. Capacity is still expressed in BTU/h or tons; the calculator applies to all of them.
Room-level (CRAC/CRAH)
Computer Room Air Conditioning (CRAC) or Air Handling (CRAH) units cool the entire room. Capacity in tons or BTU/h. Common in medium to large datacenters.
In-row / close-coupled
Units placed in or next to rack rows for targeted cooling. Good for high-density zones. Still sized by total heat load (BTU/h or tons) for the zone they serve.
Liquid cooling
Direct or indirect liquid cooling (e.g. rear-door heat exchangers, direct-to-chip). Removes heat more efficiently; total heat load in watts/BTU/h still drives chiller or dry cooler sizing.
Rack-level (ACU)
Small air conditioning units per rack or pair of racks, often used in small server rooms or edge sites. Rated in BTU/h; sum per-rack load to size.
Typical values and reference table
Use this table to cross-check the calculator or estimate capacity for common scenarios. Values use the formula BTU/h = watts × 3.412 and tons = BTU/h ÷ 12,000.
| Load | Power (W) | BTU/h | Tons |
|---|---|---|---|
| 1 rack (3 kW) | 3,000 | ~10,236 | ~0.85 |
| 1 rack (6 kW) | 6,000 | ~20,472 | ~1.7 |
| 10 kW room | 10,000 | ~34,120 | ~2.84 |
| 50 kW room | 50,000 | ~170,600 | ~14.2 |
| 100 kW datacenter | 100,000 | ~341,200 | ~28.4 |
Redundancy and safety margins
For critical facilities, cooling is often redundant. N+1 means one extra unit: if you need N units to meet the load, you install N+1 so that one can fail or be maintained without losing capacity. 2N means full duplication. In N+1, each unit must be able to handle the full load (or at least the load with one unit down), so size each CRAC for total BTU/h, not total divided by number of units.
Add 10–20% to the calculated heat load for peaks, future growth, and measurement uncertainty. If the room has lighting or people in the same space, add a few percent more. The calculator lets you enter a margin (e.g. 110 for 10%%, 120 for 20%%).
Best practices
- Use measured or nameplate power for accuracy; sum all IT load in the zone (rack or room).
- Add 10–20% margin for peaks, future growth, or lighting/humans if in the same space.
- For redundant cooling (N+1), size each unit for the full load so one can be down.
- Account for PDU and UPS losses: a few percent of total power also becomes heat in the room.
- Prefer hot/cold aisle layout and containment to improve cooling effectiveness and efficiency.
- Monitor intake temperatures and humidity; set alerts to catch under-capacity or failures early.