Calculator Inputs
Pick a mode, enter your heat data, and calculate your zone.
Example Data Table
These examples show how heat days translate into heat zones.
| Example location | Heat days (above 30°C) | Estimated zone | Planning note |
|---|---|---|---|
| Coastal garden | 12 | Zone 3 | Mild summers; many cool-season crops thrive. |
| City backyard | 55 | Zone 6 | Heat-tolerant ornamentals reduce stress in midsummer. |
| Dry inland plot | 92 | Zone 8 | Mulch and drip irrigation help stabilize moisture. |
| Subtropical landscape | 165 | Zone 10 | Shade cloth protects sensitive seedlings and herbs. |
| Hot desert yard | 230 | Zone 12 | Select heat-adapted plants and provide deep watering. |
Example values are illustrative. Use local weather records when possible.
Formula Used
A heat day is counted when the daily maximum temperature is greater than your threshold (commonly 30°C / 86°F).
Heat Days = number of days where Tmax > Threshold. The estimated heat zone is then assigned using standard day-count bands: 1: <1, 2: 1–7, 3: 8–14, 4: 15–30, 5: 31–45, 6: 46–60, 7: 61–90, 8: 91–120, 9: 121–150, 10: 151–180, 11: 181–210, 12: >210.
For best accuracy, use multiple years and average your counts.
How to Use This Calculator
- Select a mode: quick counts, temperature list, or CSV upload.
- Confirm your unit and threshold (default 30°C / 86°F).
- Enter your data, then click Calculate.
- Review the heat zone, band, and planning guidance.
- Download CSV or PDF to keep records for future seasons.
Notes and Limitations
- Heat zones indicate summer heat stress potential, not winter cold tolerance.
- Microclimates (shade, pavement, wind) can shift real plant performance.
- When comparing plants, check both heat tolerance and cold hardiness.