Sundial Template Generator

A sundial only tells the time where its hour lines were drawn for: the lines bunch towards noon in some places and spread out in others, and the gnomon must rise at the local latitude. This draws a horizontal dial for your latitude at true size, with a gnomon to cut out, and can label the lines in clock time by allowing for your longitude, time zone and summer time. Every line is checked against the shadow the gnomon actually casts, worked out separately from the sun's position at midwinter, the equinoxes and midsummer.

Latitude (°, north positive)

10° to 66° either side of the equator. One decimal place is plenty: 0.1° is about 11 km.

Dial reads

Lines every

Gnomon thickness (mm)

0 for card. A thicker plate, up to 12 mm, splits the dial along the noon line so each edge casts its own half of the day.

Paper size

Print size

Margin

Millimetres of blank edge, 5 to 40.

Turn the paper sideways

How to print this, or save it as a PDF

There is no PDF to download, and there does not need to be. Open the print command in your browser and choose “Save as PDF” as the destination. Your browser decides whether the page address and date print across the top and bottom; if they appear, turn off “Headers and footers” in the print dialog.
Set the scale to 100%, not “fit to page”. This sheet is already the exact size of the paper you chose, so anything that resizes it makes every measurement on it wrong.
Leave the paper size in the dialog set to the same one you chose here.

The dial will appear here.

What this generator does

Works out the angle of every hour line on a horizontal dial for your latitude, draws the dial and a gnomon at true size, optionally relabels the lines in clock time, and prints the equation of time for the year. The sunrise and sunset calculator gives times; this makes the instrument.

How to use this tool

Enter the latitude (north positive). For clock time, choose Clock time and add the longitude (east positive), the winter time zone and whether to label for summer time.
Choose lines every hour, half hour or quarter hour, and the gnomon's thickness if it is thicker than card.
Press Make the dial, read the check line, then print both sheets at 100% and measure the 50 mm bar.
Glue the gnomon upright along the noon line with its angled corner at the dial's centre, set the dial level, and turn it so the noon line points to true north (true south below the equator).

Understanding the controls

Latitude: 10° to 66° north or south. Nearer the equator the hour lines of a horizontal dial crowd into the noon line; beyond 66° the summer sun circles the sky and the dial would need lines all round.
Dial reads: Solar time puts noon where the sun is due south (or north). Clock time moves every line by the difference between your longitude and your time zone's meridian, four minutes for each degree, and an hour for summer time if you tick it.
Lines every: Hour, half-hour or quarter-hour lines. Only hours are numbered; the others are dashed.
Gnomon thickness: 0 for card. A thick gnomon casts the morning shadow from one face and the afternoon shadow from the other, so the dial is split along the noon line by the thickness.

Worked examples

London, latitude 51.5°, solar time: The gnomon rises at 51.5°. Hour lines from 04:00 to 20:00. The 11:00 and 13:00 lines are 11.84° either side of noon, 10:00 and 14:00 are 24.32°, 09:00 and 15:00 are 38.05°, and 06:00 and 18:00 are at right angles to it.
Edinburgh, latitude 55.95°, longitude −3.19°, UK time, summer: Edinburgh is 3.19° west of the Greenwich meridian, so in summer time solar noon — the shadow on the gnomon's line — comes at 13:13 by the clock, before the equation of time.
Sydney, latitude −33.87°, longitude 151.21°, UTC+10: A southern-hemisphere dial, drawn mirrored, with the gnomon pointing to true south. Solar noon comes at 11:55 by the clock.

Common use cases

A science lesson on the Earth's rotation and why sundials differ by latitude
A garden dial template to copy onto wood or stone
Seeing how far local solar noon is from clock noon
A holiday project that works wherever you are

How this generator works

The gnomon's sloping edge, the style, is parallel to the Earth's axis, so it rises at the latitude and points to the celestial pole. On a horizontal dial its shadow lies at an angle θ from the noon line with tan θ = sin(latitude) × tan(hour angle), where the hour angle is 15° for every hour from solar noon; the calculation uses the two-argument arctangent so lines before 6 am and after 6 pm fall on the right side. Lines are drawn from the earliest sunrise to the latest sunset of the year. In clock mode each label is moved by four minutes per degree between your longitude and your time zone's meridian, and an hour for summer time. As a check, each line is compared with a shadow worked out separately: the sun's direction is built as a vector from the hour angle, the latitude and the sun's declination at midwinter, the equinox and midsummer, and the style's shadow is projected onto the dial. The two must agree, and no line may be drawn for an hour when the sun is never up.

Assumptions this tool makes

A horizontal dial, set level, with the noon line on the true meridian.
The equation of time is from a standard approximation good to about half a minute; it is printed as a table, not built into the lines.

Limitations and good to know

Horizontal dials only: vertical, equatorial and analemmatic dials are not drawn.
The longitude correction is exact for the stated longitude; it is not looked up from a place name, and nothing finds your location for you.
Summer time is a fixed hour; dates when it starts and ends are not printed.
The dial has been checked by calculation, not tested in sunlight here. Its accuracy outdoors depends on levelling, alignment and how sharp the gnomon's edge is.

Common mistakes

Lining the dial up with a compass: A compass points to magnetic north, which can be several degrees from true north. Use the sun at local solar noon, the Pole Star, or a map.
Expecting it to agree with the clock all year: Even a perfect dial runs up to about 16 minutes fast in early November and 14 minutes slow in February. Subtract the table's value.
Gluing the gnomon the wrong way round: The angled corner sits at the dial's centre and the high end points to the pole: north in the northern hemisphere, south in the southern.

Practical tips

Print the gnomon on thick card, or use it as a pattern to cut one from wood or metal.
A dial on a flat stone or slab outdoors stays aligned better than one on a garden table.
Check the alignment once at solar noon: the shadow should lie exactly along the noon line.

Privacy and your data

The dial is made in your browser; the latitude and longitude you type are not sent anywhere. Usage counts record only that a dial was made and how many lines it had.