Birthstone Calculator
Birthstone, alternate stones, and hardness from birth month.
What it does
Birthstones pair each calendar month with a gem: January garnet through December turquoise, with a few months carrying alternates like October opal and tourmaline. Jewelers standardized the modern list in 1912 with updates since.
The tool above takes the birth month. It returns the modern stone with alternates and Mohs hardness beside them.
The default of October gives Opal with Tourmaline at Mohs 5.5 to 6.5. January gives Garnet alone at 6.5 to 7.5, while June lists Pearl with Alexandrite and Moonstone.
The list follows gem society birthstone charts with the trade association monthly guides matching each assignment. Both separate modern stones from traditional extras month by month.
How to use
- Pick the birth month.
- Read the modern birthstone first.
- Check alternates for months with several.
- Read hardness before choosing daily wear.
- Ask jewelers about traditional stones for variety.
Formula
- month
- Calendar birth month, 1 to 12.
- modern
- 1912 standardized list with later additions.
- Mohs
- Scratch hardness guiding daily wear choices.
Modern and traditional lists differ for several months: March adds bloodstone, August sardonyx, December lapis beside the modern names shown here.
Worked example
Example: October birthday
Default: month 10.
- Index: October is month 10.
- Modern stone: Opal.
- Alternate: Tourmaline.
- Hardness: Mohs 5.5 to 6.5, protective settings advised.
- Tool shows Opal, Tourmaline, Mohs 5.5 to 6.5.
Reference table
| Month | Stone | Also |
|---|---|---|
| January | Garnet | None |
| April | Diamond | None |
| June | Pearl | Alexandrite, Moonstone |
| October | Opal | Tourmaline |
| November | Topaz | Citrine |
| December | Turquoise | Tanzanite, Zircon |
Limits
- Modern list only; traditions vary by culture.
- Lookup, not science: no properties are claimed.
- Treatments change care needs within a stone.
- Prices move with source and quality, not month.
Common mistakes
- Buying soft stones for daily rings without protection.
- Confusing traditional extras with modern assignments.
- Skipping hardness when sizing daily wear.
- Trusting month meanings as gem facts.
- Ignoring treatments in care routines.
Try it yourself
Quick checks. Answers sit tucked under each question.
January?
Garnet, sole modern stone, Mohs 6.5 to 7.5.
June?
Pearl with Alexandrite and Moonstone beside it.
April?
Diamond at Mohs 10, the hardest daily wear.
Questions
What is my birthstone?
Pick the month: October is Opal with Tourmaline, January Garnet, April Diamond.
Why do some months have several?
Later additions joined originals: June, August, October, November, and December carry extras.
Modern versus traditional?
Modern is the 1912 standardized jeweler list; traditional adds older stones per month.
Which are toughest?
Diamond 10, sapphire and ruby 9, topaz 8: safest for daily rings.
Softest birthstones?
Pearl near 2.5 to 4.5 and opal near 5.5 to 6.5 want protective settings.
Who standardized the list?
American jewelers in 1912, with later additions like tanzanite and spinel.