AC Tonnage Calculator

Construction

The AC Tonnage Calculator estimates the cooling capacity an air conditioner needs for a space, in tons. It multiplies the floor area by an assumed cooling load per square foot and divides by 12,000 BTU/hr (one ton of cooling). Use it as a quick sizing guide before a full Manual J load calculation.

Formula

Tonnage = (Area × BTU/sqft) ÷ 12,000
  • One ton of cooling equals 12,000 BTU/hr of heat removal.
  • Formula: Tonnage = (Area × BTU/sqft) ÷ 12,000.
  • A common rule of thumb for typical residential rooms is 20 BTU/hr per square foot.
  • Rooms with high ceilings, lots of windows, or a sunny orientation need more BTU/sqft; well-insulated or shaded rooms need less.
  • This is a quick estimate only. A full Manual J calculation accounts for insulation, windows, climate zone, and occupancy.

Example Calculation

Inputs
  • Area (sq ft): 2000
  • BTUs per Sq Ft: 20

For a 2,000 sq ft space at 20 BTU/hr per sq ft: 2,000 × 20 = 40,000 BTU/hr, which is 40,000 ÷ 12,000 ≈ 3.3 tons of cooling.

Frequently asked questions

What is AC tonnage?
Tonnage describes an air conditioner's cooling capacity. One ton equals 12,000 BTU/hr of heat removal — it is not the weight of the unit.
How many BTU per square foot should I use?
A common rule of thumb is about 20 BTU/hr per square foot for typical rooms, rising for sunny rooms, high ceilings, or hot climates and falling for well-insulated or shaded spaces.
Is this a substitute for a Manual J calculation?
No. This is a quick estimate. A proper Manual J load calculation accounts for insulation, windows, orientation, occupancy, and climate, and is recommended before buying equipment.
Why does oversizing matter?
An oversized AC short-cycles, cools unevenly, and removes less humidity, which wastes energy and reduces comfort. Right-sizing is more efficient.
How do I convert tons to BTU?
Multiply tons by 12,000. For example, 3 tons equals 36,000 BTU/hr.