The length: It should be of a proper length which will indicate it has been harvested at the right time. Most butternut squash will reach a length of 8–12 inches (20–30 cm).
The stem: When a butternut squash ripens, the stem will turn color, from green to brown. Look for a firm deep brown stem. Avoid choosing a butternut squash from the store without a stem at all (it indicated the squash is overripe).
Texture: Avoid choosing a squash with cuts, soft spots, or brown marks. A few blemishes on the surface are fine. Ripe butternut squash should also feel hard like an unripe avocado.
Test with your fingernail, by pushing gently into the surface, it should feel hard and difficult to push through. Tap on it: Look for a hollow sound (just like with watermelon).