Ancho chiles are mild to moderately spicy, ranking around 1,000 to 2,000 Scoville Heat Units (SHU) on the Scoville scale. For comparison, that puts them well below a jalapeño (2,500–8,000 SHU) and far below a habanero (100,000–350,000 SHU), making anchos one of the gentler dried chiles used in cooking.
An ancho chile is simply a dried poblano pepper — "ancho" means "wide" in Spanish, referring to its broad, flattened shape. Because the poblano itself is already a mild pepper (1,000–2,000 SHU), drying it doesn't significantly increase its heat level, though drying does concentrate and deepen its flavor. Most people describe ancho chiles as having a rich, slightly sweet, raisin-like or dried-fruit flavor with mild smokiness and only a gentle, lingering warmth rather than a sharp burn.
This mildness is why anchos are prized more for flavor and color than for heat in dishes like mole sauces, adobo, chili powders, and braises. They add depth, a touch of sweetness, and a deep reddish-brown hue to sauces without overwhelming a dish with spiciness. Cooks often pair anchos with hotter chiles (like chipotle or arbol) when they want to layer in more heat while keeping the ancho's fruity, mellow base flavor.
It's worth noting that heat levels can vary somewhat between individual peppers due to growing conditions, soil, and genetics, so some anchos may taste slightly hotter or milder than others even within the same batch. But generally, anchos are considered a beginner-friendly, low-heat chile suitable for those who want rich flavor without much fire.