You're standing at a gas station in Marathon, probably grabbing a Pub Sub or some overpriced sunscreen, and you look at your GPS. It says about an hour. You think, "Easy." But the reality of how far from Marathon to Key West is rarely about the raw mileage. It’s about the rhythm of the Overseas Highway, the psychological weight of the Seven Mile Bridge, and the fact that a single broken-down boat trailer can turn a 50-mile sprint into a three-hour ordeal.
Technically? It’s roughly 50 to 55 miles.
Most people measure the distance from the heart of Marathon (near Mile Marker 50) to the "Southernmost Point" buoy in Key West (Mile Marker 0). If you’re at the Florida Keys Marathon International Airport, you’re looking at almost exactly 50 miles of pavement. But if you're starting up near the Vaca Cut Bridge on the north end of town, add another five or six miles to that tally.
The actual drive: Breaking down the miles
The drive is basically one long, narrow ribbon of U.S. 1. You leave the "city" feel of Marathon—which is really just a collection of bait shops, grocery stores, and resorts—and immediately hit the Seven Mile Bridge.
This is where the distance feels different.
The Seven Mile Bridge is roughly 6.79 miles long. It’s a straight shot. There is nowhere to pull over. If you get stuck behind a slow-moving RV or someone staring a little too intently at the turquoise water of the Moser Channel, those seven miles feel like twenty. It’s one of the longest segmental bridges in the world, and it connects the Middle Keys to Little Duck Key.
Once you’re off the bridge, you enter the Lower Keys. This is the "wild" part of the drive. You’ll pass through places like Big Pine Key, Summerland Key, and Cudjoe Key. The speed limits here change constantly. You’ll go from 55 mph down to 45 mph, and then—crucially—down to 35 mph if you’re driving through the Big Pine Key deer protection zone at night.
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Local law enforcement does not play around in the Big Pine area. The Key Deer are endangered and tiny, and the Monroe County Sheriff’s Office is very good at spotting anyone trying to shave five minutes off their arrival time.
Why the "time" is a lie
If you ask Google Maps how far from Marathon to Key West, it usually quotes about 1 hour and 10 minutes.
That is a best-case scenario.
In reality, you have to account for the "Lower Keys Shuffle." Between Mile Marker 30 and Mile Marker 10, the road is dotted with stoplights and local traffic. You’re passing the Square Grouper Bar and Grill (stop there for the coconut pink shrimp, seriously) and the Baby’s Coffee stand. Every time a boat trailer turns onto the highway, the whole line slows down.
Then there’s the entrance to Key West itself.
Around Mile Marker 5, the road splits into North Roosevelt Boulevard and South Roosevelt Boulevard. If you take the North route (the most common), you’re hitting a gauntlet of traffic lights, shopping centers, and pedestrians. This final 5-mile stretch can take 20 minutes on its own during peak season.
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The landmarks that mark your progress
Driving in the Keys is all about the Mile Markers (MM). It’s how everyone gives directions.
- MM 50 to 47: You’re leaving Marathon. You’ll pass the Turtle Hospital and Pigeon Key.
- MM 47 to 40: You are on the Seven Mile Bridge. Look to your right to see the Old Flagler Bridge, which is now a world-class walking and biking path.
- MM 37: Bahia Honda State Park. If you have an extra hour, stop here. The beach is widely considered the best in the entire island chain.
- MM 30: Big Pine Key. This is roughly the halfway point between Marathon and Key West.
- MM 10: Big Coppitt Key. You’re getting close, but the speed traps here are legendary.
- MM 5: Stock Island. This is the industrial heart of the area, full of marinas and the best "real" food in the region.
- MM 0: The end of the road.
Most visitors don't realize that the "Southernmost Point" isn't actually at Mile Marker 0. The official end of U.S. 1 is at the intersection of Whitehead Street and Fleming Street. The famous buoy is actually a few blocks away.
Seasonality and the "Island Time" factor
The distance doesn't change, but the difficulty does.
During "Season" (January through April), the volume of cars on U.S. 1 increases by a staggering percentage. During Fantasy Fest in October or the 4th of July, the road becomes a parking lot. If you are trying to figure out how far from Marathon to Key West during a holiday weekend, double your time estimates.
Also, watch the weather. A heavy rainstorm in the Keys isn't like a storm on the mainland. The visibility on the bridges drops to near zero, and because there is no shoulder on many sections of the road, traffic slows to a crawl.
Does the shuttle make sense?
If you don't want to drive, there are options. The Key West Transit "Lower Keys Shuttle" runs between Marathon and Key West multiple times a day. It’s cheap—usually around $4—and it stops at most major points along the way.
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Is it faster? No. It’s slower because of the frequent stops. But it allows you to look at the water instead of the bumper of the Ford F-150 in front of you.
There are also private "Keys Shuttles" that run from Miami and Ft. Lauderdale, stopping in Marathon on their way to the Southernmost City. These are more comfortable but significantly more expensive.
Safety and the "Conch Republic" mindset
One thing people often overlook when asking about the distance is the physical toll of the sun. Even inside a car, that Florida sun beating through the driver’s side window for an hour can be draining.
Stay hydrated.
The road is also notoriously dangerous at night. While it’s only 50 miles, the lack of streetlights in the Lower Keys makes for a very dark drive. Combined with potential wildlife (deer) and the occasional impaired driver returning from a night on Duval Street, the "short" drive from Marathon can be stressful after dark.
Honestly, the best way to handle the distance is to stop thinking about it as a commute. If you treat the 50 miles as a "transit phase," you’ll hate it. If you treat it as part of the vacation—stopping at the No Name Pub or checking out the Blue Hole on Big Pine—it’s one of the best drives in America.
Actionable steps for your drive
To make the most of the trip from Marathon to Key West, follow these logistical tips:
- Time your departure: Leave Marathon before 9:00 AM or after 6:00 PM to avoid the heaviest "day-tripper" traffic.
- Fuel up in Marathon: Gas prices are almost always lower in Marathon than they are in Key West. Top off your tank before you hit the Seven Mile Bridge.
- Download your maps: Cell service can be spotty on the longer bridges and in certain pockets of the Lower Keys. Don't rely on a live stream for your navigation.
- Monitor "The 1": Check local Facebook groups or Florida 511 for accident reports. Since there is only one road in and one road out, a single accident can close the highway for hours.
- Check the wind: If you’re driving a high-profile vehicle like a camper or a van, check the wind speeds. Crossing the Seven Mile Bridge in a 25 mph crosswind is a white-knuckle experience you probably want to avoid.
The distance is fixed at about 50 miles, but the experience is entirely up to the tide, the traffic, and your patience. Plan for 90 minutes, hope for 60, and keep your eyes on the water.