How many BTU do I need per square foot?

A common rule of thumb is about 20–25 BTU per square foot for an average home in a moderate climate, less in cool climates (18–22) and more in hot climates (28–35 or higher). This is only a ballpark — real sizing depends on insulation, windows, orientation, infiltration, and local design temperatures.

How many tons of AC for 2,000 square feet?

Using the rule of thumb, 2,000 sq ft × 20–25 BTU/sq ft is roughly 40,000–50,000 BTU/h, or about 3.5–4 tons in a moderate climate. But this is a rough estimate only — a Manual J load calculation often yields a meaningfully different (frequently smaller) number.

Is this calculator accurate enough to size equipment?

No. Rule-of-thumb square-footage sizing can be off by 30–50% because it ignores insulation R-values, window quality and orientation, air infiltration, duct losses, and local design conditions. Use it only for early budgeting; always get a Manual J residential load calculation (or a commercial load analysis) before purchasing equipment.

Why is oversizing AC a problem?

An oversized system short-cycles: it cools the air quickly but doesn't run long enough to remove humidity, leaving the space cold and clammy. It also wears out faster and costs more upfront. A right-sized system from a proper load calculation runs longer, dehumidifies better, and lasts longer.

HVAC Load Estimate Calculator (Square Footage)

Free rule-of-thumb HVAC sizing calculator. Estimate ballpark cooling BTU and tonnage from square footage and climate — for quick budgeting only, not a substitute for a Manual J load calculation.

This is a rough estimate, not a system design. Rule-of-thumb sizing can be off by 30–50%. It does not replace a Manual J load calculation and must never be used to actually select equipment. Use it for ballpark budgeting only, then have a professional run a Manual J (residential) or load analysis (commercial) before buying anything.

How the square-footage estimate works

A long-standing field rule of thumb sizes cooling from conditioned area and a per-square-foot BTU factor:

Estimated BTU/h ≈ Area (sq ft) × Climate factor (BTU/sq ft) × Insulation modifier

Tons = BTU/h ÷ 12,000

Climate	BTU/sq ft
Cool	18–22
Moderate	20–25
Hot	28–35
Very hot / desert	40–50+

Insulation modifier: tight/new construction ≈ ×0.85, average ≈ ×1.0, older/leaky ≈ ×1.3.

Worked example

2,000 sq ft, moderate climate (≈22 BTU/sq ft), average insulation:

2,000 × 22 × 1.0 = 44,000 BTU/h ≈ 3.7 tons — a ballpark only.

Why this is only a starting point

Rule-of-thumb sizing ignores the things that actually drive a load: insulation R-values, window U-factors and orientation, air infiltration, duct losses, internal gains, and local design temperatures. As a result it can be off by 30–50%, and it tends to oversize — which causes short cycling, poor dehumidification, and premature wear.

Always commission a Manual J residential load calculation (or a commercial load analysis) before selecting equipment. Most manufacturers’ warranties and many building codes now require a certified load calculation. Use this tool only for early budgeting and feasibility.

How FieldPad helps in the field

Give a customer a ballpark here, then move the real work into FieldPad — log the equipment, attach the proper load calculation, and turn an accurate, right-sized recommendation into a signed estimate. One offline-ready app, full history on every client and system.

HVAC Load Estimate Calculator (Square Footage)

How the square-footage estimate works

Worked example

Why this is only a starting point

How FieldPad helps in the field

Stop Re-Running These Numbers by Hand