Kepler's Third Law Calculator

The Kepler's Third Law Calculator substitutes your inputs (Semi-major axis (AU), Star mass (M☉)) into the standard expression: Period (years) = √(Semi-major axis (AU)^3 ÷ Star mass (M☉)). Every variable is read straight from the fields on this page, and the result is computed the moment you enter the values.

1. 1

   Step 1

   Type the required astronomical variables.

2. 2

   Step 2

   Hit "Calculate" and the result is computed automatically.

3. 3

   Step 3

   Save or share the result as needed.

4. 4

   Step 4

   The breakdown lists your inputs — Semi-major axis (AU), Star mass (M☉) next to the value computed by Period (years) = √(Semi-major axis (AU)^3 ÷ Star mass (M☉)); read it before relying on the number.

5. 5

   Step 5

   Adjust one input at a time and compare scenarios: change Semi-major axis (AU) and re-run to see which variable moves the kepler's third law result most.

• 1

  The Kepler's Third Law Calculator needs every variable in consistent units — Semi-major axis (AU), Star mass (M☉) — before the standard formula returns a valid result, so check each field's unit before entering values copied from elsewhere.

• 2

  Read implausible results with suspicion: if the Kepler's Third Law output sits orders of magnitude away from your expectation, re-read the inputs — a misplaced decimal or two swapped fields explains most nonsensical answers.

• 3

  Treat the Kepler's Third Law output as a computed reference, not a guarantee: where money, health, or compliance is involved, have a professional confirm the inputs and the interpretation before you act on the number.

• Zero and negatives can sit outside the formula's domain: zero star mass (m☉) may make the Kepler's Third Law undefined, and a negative semi-major axis (au) still returns a number. Check each input is inside the range the quantity allows.

• Percentage conventions differ by field: some Kepler's Third Law inputs expect star mass (m☉) as a whole number (5 for 5%), others as a decimal (0.05). The two forms are off by ×100 — match the field's label or example.