AC tonnage calculator
Floor area, insulation, occupants and heat-producing equipment: you get the cooling load in BTU/h, tons and kW, and the stock unit size to install.
Recommended unit size
11942.496 BTU/h
Net measurement: 10338.789 BTU/h
- Recommended unit size11942.496 BTU/h
- Estimated cooling load10338.789 BTU/h
- Frigories per hour2601.5 frig/h
- Tons of cooling0.86 tons
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How it's calculated (visible formula)
kW = area × W/m² (insulation) + 100 W per extra occupant + 50% of equipment; pick the next stock size
- Net geometric measurement, no waste.
- Adjustable waste % for cuts and breakage.
- Purchase rounded up to sellable units (boxes, bags, buckets, boards).
How to calculate it, step by step
- Measure the room's floor area.
- Weigh insulation, orientation and glazing to pick a load ratio.
- Add about 340 BTU/h (100 W) per regular occupant above two.
- Add equipment heat (computers, TVs, cooking).
- Pick the next larger stock size.
Worked example: 270 sq ft bedroom, average insulation, 2 people, 300 W of equipment
- 25 m² × 115 = 2,875 W
- + 50% of 300 W = 3,025 W ≈ 10,300 BTU/h
- 0.86 tons
→ A 12,000 BTU/h (1-ton, 3.5 kW) unit.
Common mistakes
- Sizing by area alone, ignoring west-facing glass.
- Oversizing — short cycles and poor dehumidification.
- Confusing cooling capacity with electrical input.
Pro tips
- Step up one size for top floors or west-facing glass.
- Mount the indoor unit out of direct sun with clear airflow.
- Choose inverter units — they modulate and use less energy.
- Check maximum line-set length between units.
From calculation to quote
Add labour, overhead and your margin, and generate the professional PDF.
FAQs
- How many BTU per square foot?
- About 20–30 BTU/h per sq ft depending on climate, insulation and sun.
- What is a ton of cooling?
- 12,000 BTU/h (3.517 kW).
- Is this a Manual J?
- No — it's a quick estimate. Use Manual J to select equipment.
- What size AC for a 500 sq ft room?
- About 12,000 BTU/h (1 ton) with average insulation.
- BTU or kW?
- Same quantity, different units: 1 kW ≈ 3,412 BTU/h.
- One mini split for two rooms?
- Only if they're open to each other; otherwise use multi-zone.
Sources and standards
Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.