Planetary Day Converter
Convert Earth days, Mars sols, and planetary days using accurate solar-day or sidereal rotation data.
Convert planetary days
How Long Is a Day on Each Planet?
A Mars solar day, called a sol, is about 24 hours 39 minutes 35 seconds. Jupiter is about 9.9 hours. Saturn is about 10.7 hours.
- Venus: its solar day is about 116.75 Earth days, while its sidereal rotation is about 243.025 Earth days.
- Mercury: its solar day is about 176 Earth days, while its sidereal rotation is about 58.65 Earth days.
Browser-only conversion from NASA / NASA-GISS day-length references. EverydayTools is not an official NASA tool.
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Earth Days to Mars Sols
A Mars solar day is called a sol. Using the NASA mean solar day, 1 Mars sol ≈ 1.027491 Earth days, so 1 Earth day ≈ 0.973244 Mars sols.
Formula: Mars sols = Earth days × 24 / 24.6597
| Earth days | Mars sols |
|---|---|
| 1 | 0.973244 |
| 5 | 4.866221 |
| 10 | 9.732443 |
| 30 | 29.197329 |
| 100 | 97.32443 |
Mars Sols to Earth Days
Reverse the same hours: Earth days = Mars sols × 24.6597 / 24. One sol is 1.027491 Earth days, or about 24 hours 39 minutes 35 seconds.
| Mars sols | Earth days |
|---|---|
| 1 | 1.027491 |
| 5 | 5.137456 |
| 10 | 10.274913 |
| 30 | 30.824738 |
| 100 | 102.749125 |
How to Use the Planetary Day Converter
- Choose the source planet.
- Choose the target planet.
- Enter the number of planetary days.
- Copy or share the result.
How Planetary Day Conversion Works
Target quantity = source quantity × source day length ÷ target day length. Both lengths use the same mode — solar day or sidereal rotation — so the units stay consistent.
A planetary day is a rotation or day-length idea. A planetary year is an orbital idea. They are not interchangeable. Jupiter’s day is about 10 hours; its year is almost 12 Earth years.
A solar day is Sun-to-Sun: the time from one local noon to the next. A sidereal rotation is one spin relative to distant stars. On Earth the difference is only a few minutes. On Mercury and Venus the difference is huge because those worlds move a long way along their orbits while they spin.
Real conversion examples
- 1 Earth day = 0.973244 Mars sols
- 1 Mars sol = 1.027491 Earth days
- 10 Mars sols = 10.274913 Earth days
- 1 Earth day = 2.417917 Jupiter days
- 1 Earth day = 0.008565 Venus days
- 1 Earth day = 0.005684 Mercury days
Planet day length table
The main converter defaults to Solar Day. Sidereal rotation is listed so you can see why Mercury and Venus look so different in the two modes. Pluto is omitted here because it is a dwarf planet — it is still available in the calculator.
| Planet | Solar Day | Sidereal Rotation | Earth-Day Equivalent |
|---|---|---|---|
| Mercury | 175.94 Earth days | 58.65 Earth days | 175.941667 |
| Venus | 116.75 Earth days | 243.03 Earth days | 116.75 |
| Earth | 24 h | 23.9345 h | 1 |
| Mars | 24.6598 h | 24.6229 h | 1.027491 |
| Jupiter | 9.9259 h | 9.925 h | 0.413579 |
| Saturn | 10.656 h | 10.6562 h | 0.444 |
| Uranus | 17.24 h | 17.24 h | 0.718333 |
| Neptune | 16.11 h | 16.11 h | 0.67125 |
Common Mistakes When Converting Planetary Days
- Confusing a planetary day with a planetary year. Age and orbit questions belong on the Age on Other Planets Calculator or the year converter.
- Confusing solar day with sidereal rotation. A Mars sol is the solar day, not the 24.6229-hour sidereal spin.
- Using Mercury’s sidereal value as its solar day. Mercury’s solar day is about 176 Earth days; its sidereal rotation is about 58.6.
- Treating a Mars sol as exactly 24 Earth hours. It is about 39 minutes 35 seconds longer.
- Assuming every “day” uses the same definition. Switch the mode when you need star-relative rotation instead of Sun-to-Sun time.
Data sources and limits
Day lengths follow the NASA / NASA-GISS Planetary Fact Sheet rotation and length-of-day references. EverydayTools is an independent calculator and is not an official NASA tool. NASA does not endorse EverydayTools.
For spacecraft navigation or mission clock synchronization, use the mission’s published timekeeping. This page is a general-purpose educational reference.
Frequently asked questions
What is a planetary day?
- A planetary day is how long a world takes to complete one solar day or one sidereal rotation. It is not a planetary year, which is one orbit around the Sun.
How long is a day on Mars?
- A Mars solar day, called a sol, is about 24 hours 39 minutes 35 seconds, or 1.0274912517 Earth days. The sidereal rotation is about 24.6229 hours.
How long is a Mars sol?
- One sol is the Mars mean solar day: about 24 hours 39 minutes 35 seconds. That is the default Mars value in this converter.
How many Earth days is one Mars sol?
- One Mars sol is 1.0274912517 Earth days — a little more than 24 hours 39 minutes.
How many Mars sols are in one Earth day?
- One Earth day is about 0.973248 Mars sols, because a sol is slightly longer than 24 hours.
How long is a day on Jupiter?
- About 9.9 hours — the shortest day among the eight planets.
Which planet has the longest day?
- Mercury has the longest solar day, about 176 Earth days. Venus has the longest sidereal rotation, about 243 Earth days.
Which planet has the shortest day?
- Jupiter. Its solar day is about 9.9 hours.
What is the difference between a solar day and a sidereal day?
- A solar day is noon-to-noon relative to the Sun. A sidereal day is one rotation relative to distant stars. They differ most on Mercury and Venus.
Why is Mercury's solar day longer than its rotation period?
- Mercury is in a 3:2 spin–orbit resonance. It rotates once every 58.6 Earth days relative to the stars, but noon returns only about every 176 Earth days.
Can I convert days between any two planets?
- Yes. Choose any pair among Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto (listed as a dwarf planet).
Does this calculator use solar days or sidereal rotation?
- Solar day is the default. Switch to Sidereal Rotation when you want star-relative spin periods.
Is a Mars day the same as a Mars year?
- No. A Mars day (sol) is one solar rotation. A Mars year is one orbit around the Sun — about 687 Earth days.
Are the calculations done in my browser?
- Yes. Amounts and results stay on your device. EverydayTools does not upload the numbers for a normal conversion.