Free HVAC Calculators for Homeowners

Size an air conditioner, furnace or mini split, work out airflow and estimate installation cost. Every tool shows the formula it uses.

  • 10 free calculators, no sign-up
  • Formulas and sources on every page
  • Plain-English explanations of the results

Quick AC Size Calculator

A fast estimate for one home or room.

Enter an area between 100 and 10,000 sq ft.
—BTU per hour
—Suggested AC size

Rule-of-thumb estimate. For insulation, windows and duct losses, use the full AC Tonnage Calculator or HVAC Load Calculator.

All HVAC Calculators

Pick a tool. Each page explains the inputs, the formula and how to read your result.

Sizing

TON
AC Tonnage CalculatorRight-size a central air conditioner in tons.
BTU
Room BTU CalculatorBTUs needed for a single room, window or portable unit.
LOAD
HVAC Load CalculatorHeating and cooling load for the whole house.
MINI
Mini Split Sizing CalculatorBTU size for each ductless zone.
HEAT
Furnace Size CalculatorFurnace BTU output your home needs.

Airflow

CFM
CFM CalculatorAirflow a room or system needs.
GRL
Return Air Grille Size CalculatorMatch grille size to CFM to avoid noise and restriction.

Diagnostics

ΔT
Delta T CalculatorCheck system performance from two temperature readings.
h
Enthalpy CalculatorTotal heat content of air from temperature and humidity.

Cost

$
HVAC Installation Cost Calculator2026 price ranges by system type, size and efficiency.

Learn the Basics

Guides that explain what the numbers mean.

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What Size HVAC System Do I Need?Why sizing matters more than brand, and how to get it right.

How Our Calculators Work

Standard formulasBased on common industry equations and rules of thumb, with sources cited on each page.
Estimates, not engineeringUse results for planning. For final equipment sizing, ask a licensed contractor for a Manual J load calculation.
Free and privateCalculations run in your browser. No sign-up, and we don’t store what you enter.
Need a technician? See our researched list of HVAC repair companies in Oklahoma City or browse HVAC repair by city.
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