Soffit Vent Calculator
How many soffit vents your intake needs.
Enter your values
Enter the required intake area in sq in.
Choose one of: 16x8 rectangular (56 sq in), 3 in round (7 sq in), Continuous strip (9 sq in per ft).
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Vents required
- 10
- Net free area each
- 56 sq in
- Total provided
- 560 sq in
- Spare capacity
- 20 sq in
Quick answer
Intake area should equal or slightly exceed exhaust area so the attic never depressurises.
vents = required intake area / NFA per vent
At a glance
| What it does | How many soffit vents your intake needs. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Required intake area, Vent type |
| Main output | Vents required |
| Formula | vents = required intake area / NFA per vent |
| Cost | Free — no sign-up, no download |
How to use the Soffit Vent Calculator
- 1Take the required intake area from a roof ventilation calculation.
- 2Pick the vent style you will install.
- 3Spread the vents evenly along both eaves, not clustered at one end.
Inputs explained
- Required intake area(sq in)
- Enter the required intake area in sq in.
- Vent type
- Choose one of: 16x8 rectangular (56 sq in), 3 in round (7 sq in), Continuous strip (9 sq in per ft).
Worked example
Using the values the calculator loads with:
Inputs
- Required intake area540 sq in
- Vent type16x8 rectangular (56 sq in)
Results
- Vents required10
- Net free area each56 sq in
- Total provided560 sq in
- Spare capacity20 sq in
Frequently asked questions
Can I have too much intake?
Extra intake is harmless and helps balance; too little is what causes moisture problems.
Do baffles matter?
Yes — insulation baffles keep the soffit path clear so the vents actually work.
What do I need to enter into the Soffit Vent Calculator?
Just 2 values: required intake area, vent type. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Soffit Vent Calculator work out the answer?
Intake area should equal or slightly exceed exhaust area so the attic never depressurises. It applies the formula vents = required intake area / NFA per vent and shows the working so you can check each step by hand.
Is the Soffit Vent Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.