Transportaton from Heathrow to Southampton England

You could take a taxi to Slough train station(8 miles from the airport)then take the train to Reading, then change trains to Southampton. Trains leave about every 30 minutes, its about an hour and forty five minutes.

The absolute easiest way to get from Heathrow to Southampton is to take the National Express bus direct. No changes. The trip takes two hours and 15 minutes. Route number 203.

The bus definitely beats the train, like Frank II says. I stupidly went by train from Heathrow to Southampton, not appreciating that there might well be a bus. So I took the Heathrow Connect train to Paddington station, then got the train from there to Reading and switched to the train to Southhampton. It wasn't much trouble switching trains at Reading[INVALID]the connecting train was only a track away and a five minute wait. But on both trains, lots of the seats were pre-reserved, so finding a place to sit was a hassle. On the way back I took the bus. Easy, peasy, no worry about other people's reserved seats and having to hoist my bag overhead into the tight overhead compartment. Just leave it stowed in the belly of the bus, nice and secure. Oh yeah, and the cost was less than half of what I paid to get to Southampton by train, and on top of that, I picked up the bus close to the University where I was staying and avoided having to schlep in to the main station. Moral of the story? You're smart to ask online here for advice, and I was dumb to just assume that the train would be the handiest mode of transport.