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Plant Hardiness Zone Lookup

Enter a USDA hardiness zone to see its minimum temperature range.

How it is calculated

Enter a whole zone number from 1 to 13. Each USDA zone is a 10 °F band of average annual extreme minimum winter temperature, and zone 1 starts at −60 °F. The tool computes

lower limit (°F) = −60 + (zone − 1) × 10
upper limit (°F) = lower limit + 10
lower limit (°C) = (°F − 32) × 5 ÷ 9

It shows the lower limit in °F and °C (the Celsius value to one decimal) and the full range in °F. A decimal such as 7.5 is rounded to the nearest whole zone (8) first, and only then is the zone checked against 1 to 13: 0.8 counts as zone 1 and 13.4 as zone 13, while anything that rounds outside 1 to 13 returns nothing. The tool only handles the number: it does not accept half-zone letters like 7a or 7b, which split each band into two 5 °F steps, and it does not look up a zone from a postcode or city.

Worked example

Zone 5. Lower limit: −60 + (5 − 1) × 10 = −60 + 40 = -20°F. Upper limit: −20 + 10 = −10 °F, so the range is -20°F to -10°F. In Celsius the lower limit is (−20 − 32) × 5 ÷ 9 = −52 × 5 ÷ 9 = −28.9 °C. A plant labelled hardy to zone 5 is expected to survive winters whose coldest nights average between −20 °F and −10 °F.

Try this example →

Common mistakes

  • Entering the zone with its letter, such as 7a or 7b. Only a plain number is accepted, so use 7 and remember that a/b halves split the range into 5 °F steps.
  • Typing the temperature instead of the zone number. Zone 5 is not 5 °F; the field wants a number from 1 to 13.
  • Reading the range as a daily forecast. It is the average of the coldest night each year, so individual winters can be colder than the lower limit.
  • Assuming a higher zone number is colder. It is the reverse: zone 1 is the coldest and 13 the warmest, so a plant rated to zone 4 tolerates colder winters than one rated to zone 7.
  • Treating the zone as the only test for a plant. It covers winter cold only, not summer heat, rainfall, soil or snow cover.

About this calculator

The USDA Plant Hardiness Zone Map divides North America into 13 zones (further split into "a" and "b" half-zones) based on the average annual extreme minimum winter temperature recorded for each area — Zone 1 is the coldest, down around -60°F, while Zone 13 stays above 60°F even in its coldest snap. This tool looks up the temperature range that defines any given zone number, in both Fahrenheit and Celsius.

Gardeners, landscapers, and nurseries rely on hardiness zones as the standard way to judge whether a perennial plant, shrub, or tree is likely to survive the winter in a given location — plant tags and seed catalogs list a hardiness range (e.g. "zones 4-8"), and matching that against your local zone is one of the first checks before planting anything meant to come back year after year.

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Comments (1)

  • Editorial team

    The zone only turns into a decision once you compare it with a plant tag. Zone 7 here means a coldest-night average from 0 °F to 10 °F, with a lower limit of -17.8 °C, so a plant rated to zone 8 is borderline there. Potted plants are more exposed than ground-planted ones, so many gardeners pick a rating a zone colder for containers. Which plants are you trying to overwinter outdoors?

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