HVAC & Room Comfort Calculators
Air conditioners and heaters are rated in BTU, and the right size is a room-math problem: about 20–25 BTU per square foot, adjusted for climate zone, ceiling height, sun exposure and insulation. The BTU calculator handles the adjustment so you buy a unit that cools, not one that cycles all day.
Why sizing matters: too big is as bad as too small
An oversized AC cools the air so fast it short-cycles and never dehumidifies — you feel cold but damp. An undersized unit runs constantly and can't keep up on hot days. The sizing rule of thumb (used in U.S. Department of Energy / ENERGY STAR guidance) starts at ~20–25 BTU per sq ft and scales with your room and climate, so the calculator is the reliable way to land in the middle.
Start from real room area
The BTU estimate only works if the square footage is right. Measure length × width of the room you're conditioning (not the whole house), and for open-plan spaces include the connected area. Pair the square footage calculator with the BTU tool for an accurate input.
Other room-sizing tools
Comfort isn't only temperature. The same "measure the room first" logic drives the TV size calculator (viewing distance vs. screen diagonal) and the curtain length calculator (window dimensions to panel widths). Measure the space, then size the purchase.