Hardiness Zone Converter: How to Find Your USDA Zone Anywhere in the World

Most American gardeners are familiar with the USDA Plant Hardiness Zone Map. It divides up the United States into numbered “hardiness zones” based on average annual minimum winter temperatures. That number enables gardeners to select perennial plants that are likely to survive the winter in their area.

But what if you garden in another country? Can you identify the USDA hardiness zone that matches your climate in Europe, Asia, Africa or Australia – and is there any benefit in doing so?

Some countries, including Canada and the UK, use their own hardiness zone systems. However, if you're researching plants online, you'll find that they are often assigned USDA zones as standard. Knowing your equivalent zone makes international plant information easier to use.

Fortunately, it's not difficult to work out your equivalent USDA hardiness zone. Once you understand how the system works, you can cross-reference local minimum temperatures with the temperature ranges shown on the USDA map to identify your zone.

About USDA Hardiness Zones

There are currently 13 USDA hardiness zones in the United States, which are designated based on the average annual extreme minimum temperature of an area. The lower the zone, the colder the winter. In Arctic Zone 1, average extreme minimum winter temperatures range from -60°F to -50°F (-51°C to -46°C). Each zone moves up in 10-degree jumps (about 5.6°C), all the way to a balmy Zone 13, where temperatures range from 60°F to 70°F (15.6°C to 21.1°C).

For greater precision, each zone is further divided into two subzones, each spanning 5°F (about 2.8°C). Zone 1a includes areas with average extreme minimum temperatures between -60°F and -55°F (-51.1°C to -48.3°C); Zone 1b includes areas with temperatures between -55°F and -50°F (-48.3°C to -45.6°C).

The USDA zones are displayed on a color-coded map of the United States, as well as individual state maps. Hotter zones are red, and colder zones are pale lavender. Most American gardeners are located within a less extreme blue, green, or yellow zone.

How to Convert Your Zone

Many of the more populated nations around the world have created their own plant hardiness maps, but they do not necessarily correspond directly to USDA Zones. To work out your equivalent Zone, you need to find out the average annual extreme minimum temperature in your area. The word "extreme" is important here, as it means the lowest temperature reached each year, not the standard daily winter average.

To match the current USDA system closely, you should look at the lowest temperature recorded in your area each year over the 30-year period from 1991 to 2020, then calculate the average of those 30 annual lows. You can usually get this data from a national meteorological or weather service.

Once you have this average, check the temperature against the table below to find out your USDA Zone.

If you're struggling to find detailed weather data, or your garden is close to a zone boundary, a minimum-maximum thermometer can help you understand its microclimate and track how cold it gets over successive winters. This Brannan digital thermometer from Amazon is a good example. Position it near the planting area rather than against the house, where readings may be warmer.

Other Weather Factors

Some countries take more than minimum winter temperatures into account when calculating hardiness zones. The USDA system is based solely on average annual extreme minimum temperature, while Canada uses a different system that also factors in things like snow depth, rainfall, and wind speed. Gardeners may therefore need to consider these factors when assessing how hardy a plant will be in their own garden.

For example, a plant that tolerates a given minimum temperature may still fail in a climate that is much wetter or drier, and cold combined with wet soil can make some plants more vulnerable.

Another factor to consider is local first and last frost dates, which will dictate the planting window for tender annual plants and crops.

Gardeners in hotter climates may also want to consider heat zones, which are based on the average number of days each year above 86°F (30°C). A perennial plant may be hardy enough to survive your winter but still struggle with prolonged summer heat.

Gardening Guides for Your USDA Zone

Now you know your equivalent USDA Zone, check our planting guides to find out which plants are likely to be suitable for for garden.

• Zone 1 & 2
• Zone 3
• Zone 4
• Zone 5
• Zone 6
• Zone 7
• Zone 8
• Zone 9, 10 & 11

Once you know your equivalent USDA hardiness zone, it becomes much easier to interpret plant information from American resources. Use it as a guide, alongside your local climate and garden conditions, to make the best planting choices for your yard.