AC Tonnage Calculator — Cooling-Load Screening
Turn a floor area and a cooling-load density you can stand behind into kW and TR, then add the outdoor-air, latent and process loads you have assessed separately — so nothing is hidden inside a thumb rule.
What this tool estimates
The cooling load of one space in kW (thermal) and TR: its floor area times the sensible W/m² you choose and justify, plus the outdoor-air/latent load and the process heat you have assessed separately.
What it cannot decide
- Which AC system or machine to buy — selection needs a room-by-room heat-load calculation.
- Whether your W/m² is right for this space. The tool has no figure of its own: you choose it and say where it comes from.
- The outdoor-air or latent load itself — enter it from a separate assessment, and count it once.
- Diversity between rooms, standby capacity or a safety margin. None is added.
Result
You said your W/m² already includes the outdoor-air load, and you have also entered a separate outdoor-air and latent load. If both cover the same fresh air it is counted twice: enter 0 for the separate load, or use a W/m² that leaves outdoor air out.
The W/m² is your own assumption. The arithmetic is exact, but the answer is only as good as that figure — a heat-load calculation for the space should replace it before equipment is chosen.
| Step | Value |
|---|
| Component | kW (thermal) | Share |
|---|
| W/m² | Total kW | TR |
|---|
Method version 6 October 2026. A screening estimate, not a design: see the limits below.
How this calculator works — and where it stops
What it calculates
A screening cooling load for one space, in kW (thermal) and TR: its floor area times a sensible load density you choose and justify, plus the outdoor-air/latent load and the process heat you have assessed separately — with the share each part contributes.
Inputs
- Floor area, in m² or ft².
- Sensible room-load density in W/m² — the room's own load from envelope, people, lighting and small power. It comes from a heat-load calculation for this or a comparable space, your consultant's brief, or measurements on a similar space in operation. There is no built-in figure, and you say which of these yours is.
- Whether that W/m² already includes the outdoor-air load.
- Outdoor-air and latent load in kW, assessed separately — 0 if your W/m² already covers it.
- Process and equipment heat released into the space in kW, where the W/m² leaves it out — 0 if there is none.
Method
- The floor area is converted to m² (1 ft² = 0.09290304 m²).
- Area-based load (kW) = floor area (m²) × W/m² ÷ 1,000.
- Total cooling load (kW thermal) = area-based load + outdoor-air and latent load + process and equipment heat.
- TR = total kW ÷ 3.516853 (1 TR = 12,000 BTU/h); BTU/h = kW ÷ 0.00029307107.
- Where you say the W/m² already includes outdoor air and also enter a separate outdoor-air load, the result is flagged as a possible double count — it is not silently adjusted.
- Sensitivity: the total is recomputed with the W/m² 10% and 20% either side, holding the separately assessed loads.
Assumptions
- The W/m² is the room's sensible load at design conditions, and its source is yours: the tool only does the arithmetic.
- The separately assessed loads peak at the same time as the room load. Where they peak at different times, adding them overstates the total — a diversity judgement for the designer.
- No safety margin, diversity between rooms or standby capacity is added.
Limitations
- A screening figure for budgets and plant-space reservation, not for selecting equipment: that needs a room-by-room heat-load calculation with the envelope, glazing and orientation, outdoor design conditions, occupancy, lighting and equipment schedules.
- It does not calculate the outdoor-air or latent load. Enter it from a separate assessment, and count it once — inside the W/m² or as the separate load, never both.
- It does not choose a system (split, VRF, ductable or chilled water) or size a central plant serving several spaces.
- Kilowatts here are heat to be removed (thermal), not the electricity the equipment will draw.
Worked example
Produced by running this calculator with the inputs below.
Inputs
- Floor area 100 m²
- Sensible load density 120 W/m² — the plan's test input, entered as an unjustified assumption, not a recommendation
- Outdoor-air and latent load 5 kW, assessed separately
- Process and equipment heat 0 kW
Working
- Area-based load = 100 × 120 ÷ 1,000 = 12 kW.
- Total = 12 + 5 + 0 = 17 kW (thermal).
- TR = 17 ÷ 3.516853 = 4.83 TR (58,006 BTU/h).
- Spread over the floor: 17,000 W ÷ 100 m² = 170 W/m² including the separate load, or 20.69 m² of floor per TR.
Result. 17 kW of cooling load — 4.83 TR — for this 100 m² space, 71% of it from the area-based figure and 29% from the separately assessed load.
Sensitivity — what moves the answer
- The W/m² carries the answer: at 96 W/m² (−20%) the same space needs 14.6 kW (4.15 TR); at 144 W/m² (+20%), 19.4 kW (5.52 TR).
- Each kW of separately assessed load adds 0.28 TR, whatever the floor area (1 ÷ 3.516853).
- Counting outdoor air twice — inside the W/m² and again as the separate load — adds that whole load to the answer; the tool flags the combination when you tell it the W/m² includes outdoor air.
How engineers use the result
As a first screen before a heat-load study: to reserve plant-room and outdoor-unit space, check the electrical provision for HVAC, and test a vendor's proposed tonnage against a density the team can defend. The breakdown shows how much of the load is fresh air and process heat — which often decides the system type.
When a professional design must replace it
Before equipment is selected or ordered: an HVAC engineer should replace the W/m² with a room-by-room heat-load calculation on the actual drawings, outdoor design conditions, occupancy, lighting, equipment and fresh-air basis, and the installed system should be tested and balanced against it.
Sources
- NIST Special Publication 811, Guide for the Use of the SI — Appendix B.9: ton of refrigeration (12,000 BTU/h) = 3.516 853 kW — unit conversion only; checked 6 Oct 2026
- National Building Code of India 2016 (BIS), Part 8 Building Services, Section 3 — Air Conditioning, Heating and Mechanical Ventilation — covers the design of air conditioning, outdoor and indoor design conditions and minimum ventilation rates; no figure from it is built into this tool
- BIS, Guide for Using National Building Code of India 2016 — summarises what Part 8, Section 3 covers
- Bureau of Energy Efficiency — Reports / Studies, including energy-efficient retrofit manuals for existing commercial buildings — for cutting the load before resizing plant; nothing from them is applied here
Questions people ask before using it
What do I need before using the AC cooling-load calculator?
The floor area; a sensible load density in W/m² you can justify — from a heat-load calculation for this or a comparable space, your consultant's brief, or measurements on a similar space in operation; the outdoor-air and latent load assessed separately, from the design fresh-air quantity and the outdoor design conditions; and the heat that machines, ovens, servers or other process equipment release into the space, if your W/m² does not already include it.
Which site conditions change the cooling load?
Roof and wall exposure and insulation; the area, orientation and shading of glazing; the outdoor design conditions where the building is (a humid monsoon peak loads the coil differently from a dry summer peak); how many people use the space and for how long; lighting and equipment heat; process heat and doors or shutters left open; and how much fresh air the space must take. A W/m² from a space that differs on these points will not transfer to yours.
What should I send an HVAC engineer for a heat-load review?
The layout with room uses and areas, ceiling heights, the wall, roof and glazing construction with orientation, occupancy and operating hours, lighting and equipment schedules with their heat output, any temperature or humidity the process needs, the fresh-air basis, and data on existing HVAC — capacities, age and where it falls short.
Optional: ask an engineer to look at it
The result above is yours with no form. If you want an engineer to check it against your drawings, schedules or bills, send a request. Nothing is sent until you press the button.
Request saved
It reached our team with exactly what the preview showed. An engineer will use the number you gave if they need your drawings or data.
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