USDA Plant Hardiness Zone Calculator
The USDA Plant Hardiness Zone Map is the standard guide for determining which plants can survive winters in your area. Every zone corresponds to a 10°F (5.6°C) range of average minimum winter temperatures, further split into 'a' (colder) and 'b' (warmer) sub-zones. This calculator uses the official USDA temperature thresholds to place you in the correct zone and sub-zone — just enter your region's coldest winter temperature in °C.
The USDA Plant Hardiness Zone Map divides North America into 13 zones (1–13) based on average minimum winter temperature. Zone 6 covers -23.3°C to -17.8°C (−10°F to 0°F), Zone 7 covers -17.8°C to -12.2°C (0°F to 10°F), and Zone 8 covers -12.2°C to -6.7°C (10°F to 20°F). Enter your coldest winter temperature to find your exact zone (a/b sub-zone included).
When to use this calculator
- Choosing perennials, shrubs, and trees that will survive your winters
- Matching plant tags ('Hardy to Zone 7') to your local conditions
- Planning landscape and garden projects with correct cold-hardiness data
- Understanding sub-zone differences (a vs. b) for marginal plants
- Gardeners, landscapers, and nursery professionals needing a quick zone lookup
- Confirming zone before ordering plants online
Example: New York City (minimum −12°C / 10°F)
- Minimum winter temperature: −12.2°C (10°F)
- Falls in the range for Zone 7 (0°F to 10°F)
- Upper half of zone range → sub-zone 'b'
- Result: Zone 7b
How it works
2 min readUSDA Hardiness Zone Table — All 13 Zones
The table below shows every USDA zone with its exact temperature range in both Fahrenheit and Celsius:
| Zone | Min Temp (°F) | Min Temp (°C) | Example Locations |
|---|---|---|---|
| 1a | Below −60°F | Below −51.1°C | Interior Alaska |
| 1b | −55 to −60°F | −48.3 to −51.1°C | Northern Alaska |
| 2a | −50 to −55°F | −45.6 to −48.3°C | Fairbanks, AK |
| 2b | −45 to −50°F | −42.8 to −45.6°C | Northern Canada |
| 3a | −40 to −45°F | −40 to −42.8°C | Minneapolis, MN |
| 3b | −35 to −40°F | −37.2 to −40°C | Duluth, MN |
| 4a | −30 to −35°F | −34.4 to −37.2°C | Chicago suburbs |
| 4b | −25 to −30°F | −31.7 to −34.4°C | Detroit, MI |
| 5a | −20 to −25°F | −28.9 to −31.7°C | Chicago, IL |
| 5b | −15 to −20°F | −26.1 to −28.9°C | Denver, CO |
| 6a | −10 to −15°F | −23.3 to −26.1°C | St. Louis, MO |
| 6b | −5 to −10°F | −20.6 to −23.3°C | Philadelphia, PA |
| 7a | 0 to −5°F | −17.8 to −20.6°C | Oklahoma City, OK |
| 7b | 5 to 0°F | −15 to −17.8°C | Washington, DC |
| 8a | 10 to 5°F | −12.2 to −15°C | Portland, OR |
| 8b | 15 to 10°F | −9.4 to −12.2°C | Seattle, WA |
| 9a | 20 to 15°F | −6.7 to −9.4°C | Sacramento, CA |
| 9b | 25 to 20°F | −3.9 to −6.7°C | San Diego, CA |
| 10a | 30 to 25°F | −1.1 to −3.9°C | Miami suburbs |
| 10b | 35 to 30°F | 1.7 to −1.1°C | Miami, FL |
| 11a | 40 to 35°F | 4.4 to 1.7°C | Honolulu, HI |
| 11b | 45 to 40°F | 7.2 to 4.4°C | Southern Florida |
| 12a | 50 to 45°F | 10 to 7.2°C | Puerto Rico |
| 12b | 55 to 50°F | 12.8 to 10°C | Caribbean |
| 13a | 60 to 55°F | 15.6 to 12.8°C | Tropical regions |
| 13b | Above 60°F | Above 15.6°C | Equatorial tropics |
How Zones Work
Each zone spans 10°F (5.6°C). Sub-zone 'a' is the colder half, 'b' is the warmer half — each spanning 5°F (2.8°C). A plant tagged "Hardy to Zone 7" means it should survive any winter in Zone 7 or warmer (Zones 8–13).
What Zones Don't Tell You
Zones measure cold hardiness only — they say nothing about summer heat, humidity, soil, or rainfall. The American Horticultural Society (AHS) Heat Zone Map complements the USDA system by measuring summer heat days. For reliable planting decisions, check both your hardiness zone and your AHS heat zone.
Frequently asked questions
What is the USDA Plant Hardiness Zone?
The USDA Plant Hardiness Zone (also called 'growing zone' or 'hardiness zone') is a geographic classification based on the average annual minimum winter temperature. The USDA map divides the US and Canada into 13 zones (1 = coldest, 13 = warmest), each split into sub-zones 'a' and 'b'. It is the standard reference for cold tolerance of plants in North America.
How do I convert Fahrenheit to find my zone?
Subtract 32 from the °F value and multiply by 5/9 to get °C. For example, 10°F = (10−32)×5/9 = −12.2°C, which falls in Zone 7. Or enter the °F temperature directly into your phone calculator: (°F − 32) × 0.5556 = °C.
What is the difference between Zone 7a and Zone 7b?
Both are in Zone 7, but Zone 7a is colder (minimum −20.6°C to −17.8°C / −5°F to 0°F) and Zone 7b is slightly warmer (−17.8°C to −15°C / 0°F to 5°F). A plant rated only to Zone 7b may not survive a Zone 7a winter. When in doubt, choose plants rated for the colder sub-zone.
What zones are most common in the contiguous United States?
Zones 5–9 cover most of the continental US. The Pacific Northwest is largely Zone 8–9, the Southeast Zone 7–9, the Midwest Zone 4–6, the Northeast Zone 5–7, and the Southwest Zone 8–10. Coastal areas often run 1–2 zones warmer than inland areas at the same latitude.
Can I grow Zone 8 plants in Zone 7?
Not reliably outdoors year-round. Zone 8 plants may survive mild Zone 7 winters but will likely die in a harsh one. You can try microclimates (south-facing walls, sheltered courtyards) that run 1–2 zones warmer, or grow the plant in a container you can bring indoors when temperatures drop.
Why does my garden feel warmer or colder than my zone?
Microclimates. Buildings, bodies of water, pavement, slope aspect, and tree cover all modify local temperatures. A sheltered south-facing garden bed can be 1–2 zones warmer than the surrounding area; a frost pocket (low spot where cold air collects) can be 1 zone colder. Measure your coldest spot before choosing marginal plants.
Does the USDA zone map change over time?
Yes. The USDA updated the map in 2012 and again in 2023 using 30-year climate data (1991–2020). About half of the US shifted half a zone warmer compared to the 1990 map. The 2023 update is the current official version and is what this calculator uses.
Does USDA hardiness zone apply outside North America?
The USDA zone system was designed for North America, but the temperature ranges are universal. European gardeners often use the RHS hardiness system (H1–H7) instead, and there is a general USDA-equivalent mapping. Zone boundaries based on °C thresholds apply globally — a plant hardy to Zone 7 will survive the same minimum temperature anywhere in the world.
What plants thrive in Zone 6?
Zone 6 (−23.3°C to −17.8°C / −10°F to 0°F) supports a wide range of perennials: hostas, coneflowers (Echinacea), black-eyed Susans, ornamental grasses, and most daylilies. Shrubs include forsythia, rhododendrons (cold-hardy varieties), and viburnums. Many fruit trees such as apple, pear, and cherry are also Zone 6 hardy.