Estimate required cooling in kW, BTU/hr, and tons for rooms, homes, offices, and IT spaces. Choose a room AC sizing path for HVAC planning or an IT/server room path for heat from equipment, power losses, lighting, and occupants.
Use area directly, or leave area blank and enter length and width.
1 W = 3.412 BTU/hr, 1 ton = 12,000 BTU/hr. Final equipment selection should be validated by a qualified HVAC professional.
This cooling load calculator is a simplified planning estimator, not a replacement for ACCA Manual J,
engineered HVAC design, local code requirements, or manufacturer selection software. It uses common planning
constants such as 1 W = 3.412 BTU/hr and 1 ton = 12,000 BTU/hr, plus transparent
rules of thumb for room size, ceiling height, climate, insulation, sunlight, windows, occupants, and equipment.
The room AC mode starts with a base area estimate and adjusts it for envelope and internal gains. The IT mode treats electrical power as heat, adds conversion losses, lighting, and people, then applies the same safety factor and unit conversions. Use the output to compare rough equipment sizes and to decide when a professional load calculation is worth commissioning.
| Room area | Typical base range | Common use |
|---|---|---|
| 100 to 150 sq ft | 5,000 to 6,000 BTU/hr | Small bedroom or office |
| 150 to 250 sq ft | 6,000 to 8,000 BTU/hr | Bedroom or small living room |
| 250 to 350 sq ft | 8,000 to 10,000 BTU/hr | Large bedroom or office |
| 350 to 550 sq ft | 10,000 to 14,000 BTU/hr | Living room or open-plan area |
| 550 to 1,000 sq ft | 14,000 to 24,000 BTU/hr | Apartment zone or large office |
Base area estimate: area × 20 BTU/hr per sq ft
Ceiling adjustment: base × ceilingHeight ÷ 8
Envelope adjustment: climate, temperature difference, insulation, sunlight, and room type multipliers.
Windows: windowArea × 80 BTU/hr, or windowCount × 600 BTU/hr when area is not entered.
Occupants: occupants × heatPerPerson, with 230 W or about 785 BTU/hr as the default sensible assumption.
Kitchen/equipment adjustment: kitchen rooms add about 4,000 BTU/hr; server/equipment rooms should use IT mode.
IT heat: IT watts × (1 + PSU/UPS loss/100)
Total sensible heat: IT heat + lighting/plug load + occupant heat
Safety factor: total sensible heat × (1 + safety/100)
Unit conversions: BTU/hr = W × 3.412, tons = BTU/hr ÷ 12,000, kW = W ÷ 1000
Inputs: 180 sq ft, 8 ft ceiling, average sun, two occupants, 10 percent safety.
Steps: 180 × 20 = 3,600 BTU/hr; occupants add about 1,570 BTU/hr; safety brings it near 5,700 BTU/hr.
Result: about 0.48 tons; a common recommendation is a 6,000 BTU/hr room AC after professional review.
Inputs: 320 sq ft, 9 ft ceiling, sunny west-facing windows, four occupants, 500 W plug load.
Steps: base load rises for ceiling height and sun; people and plugs add roughly 4,300 BTU/hr.
Result: commonly lands around 14,000 to 18,000 BTU/hr, or roughly 1.2 to 1.5 tons.
Inputs: 5 kW IT load, 8 percent losses, 500 W lighting, one occupant, 15 percent safety.
Steps: 5,000 × 1.08 + 500 + 230 = 6,130 W; safety gives 7,050 W.
Result: 24,100 BTU/hr, about 2.0 tons, typically a 24,000 BTU/hr dedicated cooling class.
Inputs: 25 kW IT load, 8 percent losses, 1,500 W lighting/support load, 600 W people/load allowance, 15 percent safety.
Steps: 25,000 × 1.08 + 1,500 + 600 = 29,100 W; safety gives 33,465 W.
Result: 114,100 BTU/hr, about 9.5 tons, requiring engineered airflow and redundancy planning.
A common simplified starting point is about 20 BTU/hr per square foot for an 8 foot ceiling. Adjust for climate, insulation, sunlight, windows, occupants, kitchens, and equipment.
One ton of cooling equals 12,000 BTU/hr, or about 3.52 kW of cooling capacity.
No. Manual J is a formal residential load calculation. This calculator is a planning estimate for quick sizing and comparison.
Yes. Higher ceilings increase air volume, so this calculator scales room estimates against an 8 foot baseline.
Glass and direct sun increase solar gain. Sunny, west-facing, and larger window areas increase the estimate; shaded rooms reduce it.
Yes. Use IT/server room mode for equipment watts, UPS or PSU losses, lighting, and support loads. Nearly all server electrical power becomes heat.
For early planning, 10 to 20 percent is common. Use professional engineering for critical rooms, future growth, redundancy, humidity, or strict uptime needs.
Oversized AC can short-cycle, remove less humidity, reduce comfort, and waste energy. Undersized systems can run continuously and still miss the target temperature.
No. The output focuses on sensible heat. Humidity and ventilation loads may require a more detailed HVAC design.
Yes. All calculations run locally in your browser.
Choose a mode, enter the space and load details, then compare the result in kW, BTU/hr, tons, daily kWh, and nearby common AC equipment sizes.
Almost every watt consumed by servers ends up as heat in the room.
Cooling systems are often rated in tons, a legacy of ice-based cooling.
Even with enough cooling capacity, poor airflow can create hot spots.
Older lighting systems can add noticeable heat in small equipment rooms.
Small growth or unexpected load spikes can overwhelm tight designs.
Cooling load estimates are simplified planning values. Validate final equipment selection with ACCA Manual J, engineered HVAC design, manufacturer data, and local requirements where applicable.