Mini Split Sizing Calculator: HVAC BTU Load Calculator

Overview

A Manual J Load Calculation, Made Simple

The calculator above starts from your room's square footage, then adjusts that baseline with the same factors an ACCA Manual J 8th Edition load calculation applies — outdoor design temperature for your ZIP code, ceiling height and volume, glass and doors, air leakage, ventilation, and internal gains. It returns a BTU/h load per room, the full breakdown behind the number, and the DIY mini split systems that match. Everything runs in your browser: no account, no email, nothing to download.

Want the detail? How it works walks through the method step by step, the sizing FAQ covers oversizing, rounding between sizes, and room-by-room vs whole-home, and about explains where the math comes from and what this tool is (and isn't) good for.

Reference Index

Sizing Guides & Resources