Orbital Period Calculator

Enter the central mass and orbital radius (semi‑major axis) to get the period. Bonus: circular orbital speed.
Earth around Sun M = 1 M☉, a = 1 AU → ~1 year
Moon around Earth M = 1 M🜨, a ≈ 384,400 km → ~27.3 days
ISS around Earth M = 1 M🜨, a ≈ 6,780 km from center → ~92 min
Jupiter around Sun M = 1 M☉, a ≈ 5.203 AU → ~11.86 years
Period (seconds)
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Period (hours)
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Period (days)
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Period (years)
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Circular orbital speed (m/s)
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μ = GM (m³/s²)
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Uses T = 2π √(r³ / GM) with G = 6.67430×10⁻¹¹ m³·kg⁻¹·s⁻². Assumes a two‑body system and negligible satellite mass.
Pro tip: for an ellipse, use the semi‑major axis for r. For circular orbits, r is the orbital radius. If results look wild, check your units.