Better HVAC starts with better numbers.
Calculate AC size, BTUs, airflow, duct requirements, operating costs and more—then find HVAC tools and equipment that help get the job done.
Start with the
numbers.
Quick calculators for cooling, heating, airflow, energy use and common HVAC planning questions.
AC Size Calculator
Estimate air conditioner size based on square footage and basic home characteristics.
Calculate AC size →BTU Calculator
Estimate cooling or heating capacity for a room, home or conditioned space.
Calculate BTUs →CFM Calculator
Estimate airflow requirements for HVAC systems, rooms and ductwork.
Calculate CFM →Duct Size Calculator
Estimate round or rectangular duct dimensions based on target airflow.
Size ductwork →SEER Savings Calculator
Compare estimated cooling energy use between systems with different efficiency ratings.
Compare efficiency →AC Running Cost
Estimate what an air conditioner may cost to operate based on energy use and electricity rates.
Estimate operating cost →Heat Pump Size
Estimate basic heating and cooling capacity requirements for a heat pump system.
Size a heat pump →Air Filter Guide
Understand filter dimensions, MERV ratings and common residential filter sizes.
Find the right filter →Get a quick AC size estimate.
Enter the approximate conditioned square footage below for a simple starting-point estimate. A professional load calculation should account for climate, insulation, windows, air leakage and other factors.
Open Full AC Calculator →Quick AC Size Estimate
Basic estimate using approximately 20 BTU per square foot.
Tools for diagnosing,
measuring and servicing.
Compare equipment used by HVAC technicians, installers, maintenance teams and serious DIYers.
HVAC Manifold Gauges
Compare digital and analog manifold gauge sets for HVAC service and diagnostics.
HVAC Multimeters
Multimeters and clamp meters suited to common HVAC electrical troubleshooting tasks.
HVAC Thermometers
Digital probes and temperature instruments for checking supply, return and equipment temperatures.
Field references without the clutter.
Calculator.ac can become a quick-reference toolbox for technicians—calculators, conversions, formulas and equipment guides all in one place.
Explore Tech Tools →
Understand the system
before spending money.
What Size Air Conditioner Do I Need?
Understand tons, BTUs, square footage and why proper HVAC sizing involves more than a simple rule of thumb.
SEER vs. SEER2
Understand cooling efficiency ratings and what the newer SEER2 measurement means.
Heat Pump vs. Air Conditioner
Compare how the systems work, where they differ and common factors homeowners consider.
Homeowner or HVAC tech?
Jump directly to calculators, equipment guides or field references based on what you're working on.