Royalston, Massachusetts has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2 °C (low) to 13.7 °C (high). Annual precipitation averages 1235 Millimeters. Royalston is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10.8 °C | -0.5 °C | 94.23 mm |
| February | -10.1 °C | 1.3 °C | 80.77 mm |
| March | -5.7 °C | 5.5 °C | 100.33 mm |
| April | 0.5 °C | 12.9 °C | 96.01 mm |
| May | 6.4 °C | 19.5 °C | 94.74 mm |
| June | 11.7 °C | 24.3 °C | 115.57 mm |
| July | 14.8 °C | 27.2 °C | 110.49 mm |
| August | 13.5 °C | 26.3 °C | 108.71 mm |
| September | 9.3 °C | 21.9 °C | 107.7 mm |
| October | 3.3 °C | 14.8 °C | 126.24 mm |
| November | -1.7 °C | 8.3 °C | 95 mm |
| December | -7 °C | 2.4 °C | 105.16 mm |
| Annual | 2 °C | 13.7 °C | 1234.95 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |