Free AC sizing calculator
AC Size Calculator: What Size Air Conditioner Do I Need?
Answer five quick questions about the home and get a planning BTU/h and tonnage estimate. The default lands inside the 500–600 sq ft per ton range Hales AC uses on its AC sizing guide, and every result shows its own sq ft per ton against that range.
Quick answer: What size AC unit do I need? For a typical 1,800 sq ft Pinellas County home with 8-ft ceilings, average insulation and sun exposure, and three occupants, the planning math points to about 37,000 BTU/h — roughly a 3-ton system. Insulation, ceiling height, sun, and duct condition all move that number, which is what the calculator below adjusts for.
What size AC unit do I need?
How this calculator works
This calculator applies a 20 BTU per hour per sq ft base load (typical for Pinellas County's climate), then adjusts for ceiling height, insulation, sun exposure, and occupancy — a simplified Manual J–style estimate. It cannot replace an on-site Manual J load calculation, which Hales AC performs before recommending any replacement system.
Pinellas County context
In Pinellas County's humid climate, oversizing is the most common sizing mistake: an oversized system short-cycles, leaves the home clammy, and wears out sooner. An undersized system runs constantly on the hottest afternoons. The right size holds temperature and drains humidity.
Frequently asked questions
How many BTU per square foot for AC in Florida?
A planning range of 20–24 BTU per hour per square foot covers most Florida homes once insulation, ceiling height, sun exposure, and occupancy are factored in. The calculator starts from 20 BTU/hr per sq ft and adjusts from there. For context, the Hales AC sizing guide plans 500–600 sq ft of living area per ton of cooling — the same 20–24 BTU/hr per sq ft band, since one ton equals 12,000 BTU/hr.
Is a bigger AC unit better?
No. An oversized AC cools the air quickly but shuts off before it has removed moisture — leaving the home cold and clammy in Florida's humidity — and the constant short-cycling wears the compressor. The right size is the one a Manual J load calculation supports, not the biggest system that fits the budget.
What does a 3-ton AC unit cool?
Under the 500–600 sq ft per ton planning range this site uses, a 3-ton system suits roughly 1,500–1,800 sq ft of living area in average condition. Duct design, ceiling height, insulation, window area, and sun exposure all shift the real answer — which is why the calculator adjusts for each of them.
Does ceiling height change AC size?
Yes. Cooling load scales with the volume of air being conditioned. The calculator scales its base load in proportion to ceiling height with 8 ft as the baseline, so the same floor area with 10-ft ceilings needs about 25% more capacity.
Is this the same as a Manual J load calculation?
No — this is a planning estimate. A Manual J load calculation (the ACCA standard) accounts for window orientation and glazing, duct location, air infiltration, and the exact construction of every surface. Hales AC performs a Manual J on site before recommending a replacement system size.