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A-a Gradient

Calculate A-a Gradient instantly with the exact formula and a worked example. Free online calculator — no signup.

A-a Gradient

FiO2 (0-1)
PaCO2, mmHg
PaO2, mmHg
Age, yrs
A-a gradient
9.73mmHg
PAO2 = FiO2·(760−47) − PaCO2/0.8; A−a = PAO2 − PaO2Calculate A-a Gradient instantly with the exact formula and a worked example. Free online calculator — no signup.
A−a
9,7
Norm
<14

More about: A-a Gradient

What it calculates

The “A-a Gradient” calculator computes A-a gradient in mmHg from 4 parameters: fio2 (0-1), paco2, mmhg, pao2, mmhg, age, yrs.

Used by professionals and patients to assess health metrics, dosages, and risks.

Example calculation

With parameters FiO2 (0-1) = 0.21, PaCO2, mmHg = 40, PaO2, mmHg = 90, Age, yrs = 40 the result is 9.73 mmHg (PAO2 = FiO2·(760−47) − PaCO2/0.8; A−a = PAO2 − PaO2).

How to use

  1. Enter the parameter values — every field above is adjustable with a slider.
  2. The result and related metrics are calculated automatically as you type.
  3. Use the additional metrics shown (if any) where needed.
  4. Copy the result or bookmark the page.

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FAQ

How is BMI calculated?
BMI = weight (kg) / height (m)². Example: 70 kg / (1.75 m)² = 22.9. The WHO normal range is 18.5–24.9; below that is underweight, 25–29.9 is overweight, and 30+ is obese.
Is BMI accurate for everyone?
No. BMI does not distinguish muscle from fat, so athletes may show a high BMI with low body fat. It is also less reliable for teenagers, pregnant people, older adults, and very tall or short individuals.
What are the BMI categories?
Underweight: below 18.5. Normal: 18.5–24.9. Overweight: 25–29.9. Obese class I: 30–34.9; class II: 35–39.9; class III: 40+.
What is a better measure than BMI?
Body fat percentage, waist-to-height ratio (aim for under 0.5), and waist circumference give a clearer picture of health than BMI alone.