Ask the seller if they are licensed retailer of Herman Miller furniture. If you are buying the furniture secondhand, ask if there is any documentation, like a receipt, from a Herman Miller retailer.
Measure the size of the lounge and ottoman, which have always been manufactured in the same dimensions. An authentic Eames lounge chair has a 15-degree tilt and 6-inch thick foam cushions. It should be 32 inches tall, 32.75 inches wide with a 32.75 inch depth. The ottoman is 17.25 inches tall, 26 inches wide and 21.5 inches in depth.
Check the screws and bolts. Screws are carefully hidden on a real Eames. Screws and bolts are usually quite visible on a fake.
Count the legs on your chair and ottoman. A true Eames has five legs on both pieces, while many fakes only have four.
Notice the wood and the materials. Herman Miller uses high quality 7-ply wood, such as cherry, walnut or santos palisander. The leather is upholstered individually on each cushion. Many fakes use one piece of leather to upholster the entire chair, making it all connected. The armrests on a real Eames are carefully upholstered with thick piping, and most fakes do not have this detail.
Turn over the chair to look for a Herman Miller and Eames stamp, production number and serial number. Without this, you cannot authenticate your furniture.