The biggest I've seen in a published source in the wild is an 80-fold error in a reported distance, which I think came from a series of at least three unit conversions and area/length misinterpretations.
Square Units [Explained]
Transcript Under the Cut
[Arrows point to each consecutive panel.]
[Megan is looking at her phone, with Cueball standing next to her.] Megan: This newly-described insect can devour up to a square inch of grass per day. Cueball: Oh, neat.
[Cueball is speaking to Ponytail.] Cueball: ...it eats a square inch, or 6 cm², of grass per day...
[Ponytail is speaking to Hairy.] Ponytail: ...a 6-centimeter (2½ inch) square of grass, or 36 cm²...
[Arrows now point to each consecutive conversion.] Written out of panel: ...a 36 centimeter square, or over a square foot... Written out of panel: ...a square foot, or 900 cm²... Written out of panel: ...a 900 cm (30 foot) square... Written out of panel: ...a 30 foot square of grass (900 square feet)... Written out of panel: ...a 900 foot square, or almost 20 acres... Written out of panel: ...20 acres (8 hectares, or 80,000 square meters)... Written out of panel: ...an 80,000 meter (80 km) square... Written out of panel: ...a square 80 km wide, or roughly 2,500 square miles... Written out of panel: ...a 2,500-mile square, or twice the land area of Australia, per day...
[An arrow points from the last conversion to the last panel.] [Hairbun is looking at her phone, with White Hat, Danish and Blondie standing next to her.] Hairbun: Did you hear about this insect that defoliates the entire land area of Australia twice a day? White Hat: Gosh! Danish: Wow. Blondie: I hope at least it's contained there...