Field-ready HVAC sizing
Size it right.
On the spot.
BTU cooling loads and exhaust fan airflow from room dimensions — the same formulas technicians run in the HVAC Calculator iOS app, free in your browser.
Calculators
BTU Calculator
Cooling capacity for any room from its dimensions and sun exposure — in BTU/h, tons, kW, and HP.
Ductulator
Duct sizing from CFM and friction rate — round and rectangular, with velocity check.
AC Size Calculator
What size air conditioner you need — matched to common window and mini-split unit sizes.
AC Tonnage Calculator
Tons from room dimensions, with a tons-to-BTU-to-kW chart. 1 ton = 12,000 BTU/h.
CFM Calculator
Exhaust fan airflow by room type and volume — 16 room presets with air-change rates.
HVAC Load Calculator
Room-by-room cooling load with occupants and kitchen adders — a quick pass before Manual J.
Mini Split Sizing
Match 9k–36k BTU units to room size — with honest mild-climate and hot-climate coverage columns.
Converters