CFM for 3-ton AC?
About 1,200 CFM using the 400 CFM per ton rule of thumb.
Required CFM ≈ AC tonnage × 400 CFM/ton. A 2.5-ton system typically needs about 1,000 CFM total supply airflow.
Use the calculator form above with your room size, system capacity, or appliance usage. Results update instantly in your browser — no data is sent to a server.
Concise answers for common searches — definitions, steps, and comparisons.
About 1,200 CFM using the 400 CFM per ton rule of thumb.
12,000 BTU/hr of cooling capacity equals one ton of refrigeration.
Required CFM ≈ AC tonnage × 400 CFM/ton. A 2.5-ton system typically needs about 1,000 CFM total supply airflow.
Formula
See calculator inputs and results panel for step-by-step math.Select imperial/metric, rectangle vs area, tons vs BTU, or usage presets as shown.
Type room dimensions, system tonnage, CFM, appliance watts, or electric rate.
Pick climate zone 1–5 and insulation quality for load-based calculators.
Use BTU/hr, tons, CFM, duct diameter, or seasonal cost in the results panel.
Copy results or share a link with your HVAC contractor or energy auditor.
Use Duct CFM, Duct Size, or Energy Cost calculators for a complete HVAC plan.
Input
20×15 ft · 8 ft ceiling · zone 3Output
≈ 7,500 BTU/hr cooling300 sq ft × 25 BTU/sq ft × average insulation × 1.0 height factor.
Input
2.5 tonsOutput
1,000 CFM2.5 × 400 CFM/ton = 1,000 CFM supply airflow rule of thumb.
Common real-world scenarios where this tool saves time.
12×15 ft room, zone 3, average insulation → ~9,000–11,000 BTU/hr cooling load.
2,000 sq ft home, zone 4 → ~3.5–4 tons cooling with average insulation.
3-ton system → 1,200 CFM target → 14" round trunk at 700 FPM velocity.
900 W unit, 8 hr/day, 90 days at $0.16/kWh → seasonal cost estimate for budgeting.
Step-by-step chains that connect related tools for common tasks.
From room BTU to duct airflow and diameter.
Compare portable appliance electricity spending.
| Tons | CFM at 400/ton | Notes |
|---|---|---|
| 2 | 800 | Small central system |
| 3 | 1,200 | Typical residential |
| 4 | 1,600 | Larger home |
Rule-of-thumb sizing is a starting point — ACCA Manual J is the industry standard.
Undersized ducts reduce efficiency and comfort even when tonnage is correct.
Include climate zone, insulation, ceiling height, and sun exposure — or request Manual J.
Check heating BTU/hr and balance point, not just cooling tons.
Compressors cycle — actual kWh may be lower than watts × hours suggests.
Advertisement
Residential rule of thumb: 400 CFM per ton — a 3-ton system needs about 1,200 CFM total supply airflow.
BTU ÷ 12,000 = tons, then tons × 400 = CFM using the standard conversion.
Dry climates may use 350 CFM/ton; humid climates sometimes need 450 CFM/ton for moisture removal — confirm with your designer.
Return airflow should roughly match supply CFM for balanced pressure — this calculator estimates total supply CFM.
Leaky ducts waste delivered CFM at registers — seal and test ducts; you may need more fan CFM at the air handler.
Use manufacturer fan tables at actual static pressure — this tool is a quick sizing starting point.
Tonnage and BTU values for duct CFM estimates stay on your device — EverydayTools does not upload duct-cfm calculator inputs.
Estimates only — not professional HVAC or energy audit advice. Verify with a licensed contractor before purchasing equipment.
Advertisement
Reviewed on 2026-06-28.
Same workflow or intent — pick the next step without leaving the site.
Free duct size calculator: Find round duct diameter from required CFM and target air velocity — shows calculated size and the next standard residen Runs locally in your browser — no signup.
Free BTU room calculator: floor area, ceiling height, climate zone → cooling BTU/hr, tons, and suggested CFM. Runs locally in your browser.
Free AC tonnage calculator: room size and climate → central air conditioner tons from cooling BTU load. Runs locally in your browser.
Free furnace BTU calculator: room or whole-home sq ft → recommended heating BTU/hr output by climate zone. Runs locally in your browser.
Free heat pump size calculator: room dimensions → tons with cooling and heating BTU/hr estimates. Runs locally in your browser.
Free window AC cost calculator: watts, hours per day, and $/kWh → monthly or seasonal electricity cost. Runs locally in your browser.
Frequently opened tools from the same category.
Calculate BMI from height and weight using metric or imperial units. See BMI category ranges and use it as a quick screening estimate. Runs locally in your browser when supported—no upload required for normal use.
Estimate daily calories using the Mifflin-St Jeor BMR formula and TDEE activity multipliers for maintenance, weight loss, or weight gain. Runs locally in your browser when supported—no upload required for normal use.
Free tip calculator — find tip amount, bill + tip total, and per-person share. Presets for common percentages (10%, 15%, 20%), custom %, and equal split. Runs in your browser. No signup.
What is 20% of 500? Percent increase, decrease, difference, reverse %, markup & margin—runs locally in your browser, no upload. Copy results or share a link.
Cross-category tools others open in the same session.
Free JSON formatter — paste minified or messy JSON and instantly get beautified, indented output with syntax highlighting and error detection. Browser-based, no server upload. Runs locally in your browser when supported—no upload required for normal use.
Compress JPG, PNG & WebP in your browser—up to 80% smaller, batch 25 files, 50/100/200 KB presets. Files stay on your device. No signup.
Free PDF merger — combine multiple PDF files into one document. Drag to reorder files, preview pages, and download the merged PDF instantly. No signup, fully browser-based. Runs locally in your browser when supported—no upload required for normal use.
Instantly count words, characters, sentences, paragraphs, and reading time. Great for essays, articles, and SEO writing. No signup — works as you type. Runs locally in your browser when supported—no upload required for normal use.
Guides and walkthroughs that reference this tool.
10 free browser calculators: BMI, tip, discount, overtime, GPA, compound interest. No upload—runs locally. No signup.
2026 roundup of BMI calculators—EverydayTools, CDC, NIH, Healthline, and Calculator.net compared on accuracy, privacy, units, and clinical context.
Browse full tool collections by topic.
1 ton = 12,000 BTU/hr