How to Set a Sundial | Make It Tell Real Time

A sundial must be level, aligned to true north, and corrected for your latitude, longitude, and the equation of time before it shows accurate local time.

For the full breakdown, see our best Large Sundial For Garden guide.

Sundials look simple — a stick and some numbers — but getting one right takes more than plunking it in the sun. , and a few degrees of misalignment can throw the reading by thirty minutes. Here is how to set one so it actually earns its place in the yard.

Pick the Right Spot in Full Sun

Start with the surface. The dial needs a horizontal top that stays level and won’t shift with wind or settling. A pedestal, stone plinth, or sturdy post works best — never set it on soil or loose gravel. The site must get sun from sunrise through at least mid-afternoon. Walls, trees, and shrubs that look small now will cast longer shadows as the season changes, so check the path of the sun before you commit. If you are shopping for one, a large sundial for garden use can anchor the whole setup with a built-in pedestal base that makes leveling straightforward.

Level the Dial in Both Directions

This is the easiest step and the one most people rush. Place a spirit level across the dial plate front-to-back and side-to-side. Shim the base until it is dead flat in both axes. A dial that is off by even a degree accumulates minutes of error by late afternoon. Once level, secure the base so it cannot be knocked askew by a bump or a mower.

Point the Gnomon at True North

The gnomon — the angled blade that casts the shadow — must point to true north, not magnetic north. The difference (magnetic declination) varies by location; in parts of the Pacific Northwest it can be 15 degrees or more, enough to make your dial read an hour off. Check your local declination online, then use a compass adjusted for the difference, or align the gnomon to Polaris on a clear night. The North Star sits within one degree of true north in the Northern Hemisphere, making it the most reliable field reference.

The Sundial Society emphasizes that magnetic north is the most common setup mistake. If you use a compass without correcting for declination, the dial will never read accurately no matter how carefully you do everything else.

Match the Gnomon Angle to Your Latitude

A correctly designed horizontal sundial has its gnomon set at an angle equal to the local latitude. If your area is 40° north, the gnomon should form a 40° angle with the dial plate. Some commercial dials ship with a fixed angle that may not match your latitude; if yours does not, you can shim the back edge of the dial plate to tilt the whole assembly — effectively changing the effective latitude angle. The tilt equals the difference between your latitude and the dial’s design latitude. Without this correction, the dial will read correctly only on one day of the year and be off by increasing amounts every other day.

Apply the Three Time Corrections

Sundials read local apparent solar time, which rarely matches your clock. Three corrections get you close:

• Equation of time. Earth’s orbit is elliptical, so solar days vary. The equation-of-time chart tells you how many minutes to add or subtract for any given date.
• Longitude correction. Each degree of longitude difference between your location and your timezone’s reference meridian adds or subtracts four minutes. West of the meridian means add time; east means subtract.
• Daylight saving time. If DST is active, subtract one full hour from the sun reading before marking your dial’s hour lines.

Combine all three corrections, then use the result to orient the dial. A common field method: around local solar noon, mark where the shadow falls and rotate the dial so that shadow lands on the corrected 12 position. This effectively aligns the gnomon to true north while incorporating the day’s corrections.

Common Mistakes That Wreck Accuracy

• Aligning to magnetic north without correcting for declination.
• Failing to level the base in both directions.
• Ignoring the equation of time or applying it backwards.
• Forgetting to subtract the DST hour from the final setting.
• Installing where future shade will creep in as trees grow.

None of these are difficult to fix, but each one produces errors large enough to make the dial decorative rather than functional.