Quick Load Estimator

Inputs

Floor Area (ft²)

Building Type

Climate

Estimated Results

Cooling

—

tons

Cooling

—

BTU/hr

Supply CFM

—

CFM

Heating

—

MBH

SF / Ton

—

ft² per ton

CFM / SF

—

CFM per ft²

Rule-of-thumb estimates only — not a substitute for a Manual J or block load calculation. Use for early feasibility and equipment pre-selection.

Reference — Typical Ranges

Building Type	SF / Ton	CFM / SF	Heat (BTU/SF)
Office	300–400	0.8–1.2	25–40
Retail	200–300	1.0–1.5	30–50
Restaurant	100–200	1.5–2.5	50–80
School	250–350	1.0–1.5	30–50
Medical Office	200–300	1.0–1.8	35–55
Warehouse	500–800	0.3–0.6	10–20
Hotel	350–500	0.7–1.0	20–35
Residential	400–600	0.5–0.8	20–35
Server / Data	50–150	2.0–5.0	—

Inputs, results, and method — as an Excel workbook or plain CSV.

Doing this for a whole building? See this step inside a connected AIM Works project — loads, ventilation, equipment, and Design Review in one place.

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About This Calculator

This quick load estimator converts a building’s floor area into approximate cooling tons, heating MBH, and supply CFM using rule-of-thumb factors keyed to building type and climate. Enter the floor area, pick a building type, and select a climate; the tool returns cooling capacity (tons and BTU/hr), heating (MBH), supply airflow, and the implied square-feet-per-ton and CFM-per-square-foot ratios.

It is built for early feasibility, budgeting, and equipment pre-selection — the stage before a full load calculation exists. The factors come from typical commercial practice and shift with climate, but they are deliberately coarse. A detailed Manual J or block load calculation, accounting for envelope, glazing, internal gains, and ventilation, is required for final sizing.

Formula & Method

Cooling tons	Tons = Area (ft²) ÷ (SF-per-ton ÷ climate factor)
Cooling BTU/hr	BTU/hr = Tons × 12,000
Supply airflow	CFM = Area (ft²) × CFM-per-ft²
Heating load	MBH = Area × (BTU/ft²) × climate factor ÷ 1,000

Base factors (square-feet-per-ton, CFM-per-ft², BTU-per-ft²) follow common industry rule-of-thumb ranges for each building type, then a climate multiplier scales cooling and heating. The constant 12,000 BTU/hr per ton of refrigeration is exact by definition. These are screening estimates, not a substitute for an ASHRAE load calculation.

Frequently Asked Questions

How accurate is a square-foot-per-ton rule of thumb?

Rule-of-thumb factors give a ballpark for early feasibility, but a real building can easily differ from them by 30 percent or more, so they cannot replace a load calculation. The same building type can vary widely with glazing area, orientation, insulation, internal gains, and climate. Use these numbers to pre-select equipment ranges and sanity-check a detailed Manual J or block load, not to size final equipment.

Why does a server room need far fewer square feet per ton than an office?

Cooling load is driven by internal heat. A server or data room packs dense electronic equipment that runs continuously, so it may need 50 to 150 square feet per ton, while a typical office with people, lights, and moderate plug loads needs about 300 to 400 square feet per ton. Higher internal gains mean fewer square feet per ton.

How does climate change the estimate?

Hotter, more humid climates raise the cooling load and lower square feet per ton, while cooler climates do the opposite and raise the heating load. This tool applies a climate multiplier to the base factors so a hot-south, mixed-US, or cool-north selection shifts both cooling tons and heating MBH in the right direction.

How is supply CFM estimated from square footage?

Supply airflow is estimated as floor area times a CFM-per-square-foot factor that depends on building type, ranging from about 0.3 to 0.6 for warehouses up to 2 to 5 for data rooms. It reflects typical air distribution for the space, not a load-balanced airflow, so verify it against the sensible load and a chosen supply air temperature during design.

Connect the calculation to the rest of the project.