BTU / Air Conditioner Size Calculator
Uses a simplified ACCA Manual J method to determine the right AC size. Enter room area, ceiling height, sun exposure, insulation quality, and climate to get BTUs needed, recommended tonnage, and unit cost range.
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How to Use This Calculator
- 1Enter your measurements in the fields above. Use the units shown next to each field (ft, in, etc.).
- 2Click Calculate to get your material estimate instantly.
- 3Review the highlighted result — it shows the key quantity you need to order.
- 4Use Copy Results to save your estimate, or bookmark the URL — your inputs are encoded in the link.
Pro tip: Always add 10% to your material order to account for waste, cuts, and defects.
Frequently Asked Questions
How many BTUs do I need for a 500 sq ft room?
A 500 sq ft room in average conditions with 8-ft ceilings needs approximately 10,000 BTUs. In a hot, sunny climate with poor insulation, you may need up to 14,000 BTUs. A 12,000 BTU (1-ton) window unit is a common choice.
Is it better to size up on AC?
No — an oversized AC cools the space quickly without dehumidifying adequately, leading to a clammy feeling and higher energy bills. Match the BTU to the actual load as closely as possible.