AC Cooling Load Calculator (BTU) — Free Manual J Lite

Estimate residential cooling load in BTU/hr from floor area, climate zone, insulation, sun exposure, and occupants using a Manual J-style simplified method.

  1. Enter conditioned area Provide the square footage of the space being cooled.
  2. Set climate and insulation Choose your climate zone and insulation/window quality so the calculator applies the right BTU-per-sq-ft factor.
  3. Add internal gains Enter occupants and major heat sources (kitchen, sunny rooms), which add sensible load.
  4. Read tons of cooling The result converts BTU/hr to tons (12,000 BTU/hr = 1 ton); round to the nearest standard size and verify with a full Manual J.

How many BTU do I need to cool a 1,000 sq ft house?

A rough rule is 20–25 BTU/hr per square foot, so a 1,000 sq ft home lands around 20,000–24,000 BTU/hr, or about 1.5–2 tons. Hot climates, lots of west-facing glass, or poor insulation push it higher. This is a starting estimate only — an oversized AC short-cycles and will not dehumidify, so confirm with a Manual J load calculation.

Is it bad to oversize an air conditioner?

Yes. An oversized AC cools the air quickly but shuts off before it removes enough humidity, leaving the house cold and clammy and short-cycling the compressor (which shortens its life and wastes energy). Right-sizing from a Manual J load calc — not from square-footage rules of thumb — gives longer run times and far better comfort and dehumidification.

How many square feet does a 2-ton AC cool?

A 2-ton (24,000 BTU/hr) unit typically cools roughly 900–1,300 sq ft in a moderate climate with average insulation. The range is wide because ceiling height, window area, sun exposure, and air-sealing all shift the load — use it as a sanity check against a Manual J result, not as the basis for selecting equipment.

How many BTUs do I need for my room size?

A quick starting point is 20–25 BTU/hr per square foot of conditioned space, so a 400 sq ft room lands around 8,000–10,000 BTU/hr. Sun exposure, ceiling height, insulation, and the number of occupants all shift that up or down. Enter your room details into the calculator for a Manual J-style estimate — an oversized unit short-cycles and will not dehumidify.

AC tonnage and cooling capacity calculator

This calculator converts a room or home's cooling load into both BTU/hr and tons, where 12,000 BTU/hr equals 1 ton. Enter the conditioned area, climate, insulation, and internal gains and it returns the required capacity so you can round to the nearest standard size (1.5, 2, 2.5 tons…). Confirm with a full Manual J before buying equipment.

Calculators