Warms root area approximately 10°F - 20°F over ambient temperature to improve germination process. Helps gardeners have better success rates with seedlings and cuttings. Perfect for one standard 10 in x 20 in propagation tray. Heavy-duty construction makes this mat very durable. More than 20% larger than competitive mats. This allows even warming of your entire tray. More consistent heating with fewer hot spots than other seedling heat mats. 20 watts. Dimensions: 10 in x 21 in.