Day Length on Planets Calculator
Compare solar-day and sidereal-rotation lengths for eight planets and convert a chosen number of those days into Earth hours and days.
Compare two meanings of a day: one rotation relative to the stars and one cycle in which the Sun returns to the same meridian. Select a planet and a definition, then convert any nonnegative number of those days into Earth hours and 24-hour days. The table keeps the definitions separate so slowly rotating or retrograde planets are not misrepresented.
How to use this tool
- Choose one of the eight planets.
- Select a solar day or a sidereal rotation period.
- Enter how many of the selected planetary days you want to convert.
- Read the elapsed Earth duration and compare the two reference columns.
Formula
Elapsed Earth hours = selected day count × reference period in hours; Earth days = hours ÷ 24
The periods come from the individual NASA factsheets and retain their published precision. Venus and Uranus have retrograde rotation. A negative rotation sign indicates direction; its magnitude is used for elapsed time. Giant-planet rotation periods are reference conventions, not the motion of a solid surface.
Example
One Venus solar day is 2,802 Earth hours, or 116.75 Earth days, in this table. One Venus sidereal rotation takes 5,832.6 hours. Earth’s corresponding values are 24 hours and 23.9345 hours, respectively.
Frequently asked questions
Why can a solar day differ from a rotation?
A planet also moves along its orbit as it rotates. The direction toward the Sun therefore changes relative to the stars, so the two return cycles generally have different durations.
Does this show how long the Sun is above the horizon?
No. Daylight duration depends on location, season and geometry. Here solar day means a full solar cycle, including the interval commonly described as night.
Why are some solar and rotation values identical?
The difference can be smaller than the precision published in the reference table. The calculator retains those supplied numbers instead of inventing additional measured precision.
Sources
Last updated: 2026-10-30