If there's one style Reese Witherspoon likes to wear when transitioning from summer to fall, it's a cardigan. Last August, The Morning Show star was spotted wearing a gray cardigan while jetting off on a trip.

And recently, she brought out the go-to style while shopping in Los Angeles. The actress opted for an oversized brown cardigan, which she styled with a crossbody bag (a Hollywood favorite right now), straight-leg jeans, and open-toe block-heeled sandals.

A cardigan is smart to wear in the fall because you never know when the weather will shift. Plus they're easy to layer over thinner tops, whether you dress them down with leggings or dress them up with jeans. Taylor Swift, Jennifer Garner, and Nicole Kidman have worn the style, too.

Need to upgrade your old cardigan? You can wear these similar styles from Amazon, Nordstrom, Lulu's, and more all fall long -- and they start at just $20.

For those looking to copy Witherspoon's Los Angeles look, you can get a similar cardigan at Amazon for just $20 when you use a coupon. The sweater has eye-catching buttons, so you can easily wear it buttoned up over T-shirts and tank tops for extra warmth. Bonus: You'll find two functional pockets on the front.

Just like a little black dress, everyone needs a little black cardigan. This cropped one from Amazon reminds us of the sweater Swift wore last fall. The shorter length makes it ideal for wearing with high-waisted jeans and skirts. And one reviewer said that it's great for different temperatures: "The material is extremely soft and is not too heavy."

Oversized cardigan sweaters give you a sweatshirt-like feel but with a little more elegance. The roomy silhouette and chunky long sleeves on this option make it layer-friendly, while the deep front pockets are practical. It's available in 21 colors like nutmeg, green, and pink. And right now, you can snag it for more than half-off.

Sweater weather is upon us. Stock up on these Witherspoon-inspired cardigans before the weather really starts to take a dip.