Heathrow, for United fight LHR to SFO, how much time to allow

Allow at least 3 for flights to US.

And they're serious about the size of your carry-on Ziploc and what's in it. For example, I wouldn't leave any stray Chapstick in the bottom of your backpack, etc. I've seen (and sadly, experienced) details like that lead to delays at security.

As a side note, transiting from LAX to ZUR through LHR was efficient but that new terminal at LHR is so big that you have to take internal travel into account. Directional signposts not only have arrows but estimated walking times, which can be quite lengthy!

And yes, better safe than sorry, take advantage of offered Ziploc bags and put every possible thing in your carryon that might cause an issue into them.

Just did this flight 2 weeks ago and we miraculously got through it in 90 minutes - don't recommend doing it the way we did: dropped off rental car at Terminal 5. Had no idea what terminal United was when we exited carpark. Finally tracked down worker who transported people by wheelchair and told us it was terminal 2. Rushed to Heathrow Express - only to wait 13 minutes for next train. Up to check-in @ United to secure luggage tags for checked-luggage and boarding pass. Make sure you have your confirmation #! Directed to weigh luggage then reprimanded for not checking with worker at end of queue to get sticker for passport. My sister-in-law did not get this sticker and had to go back; lucky we asked her almost immediately if she got a sticker when she questioned why it took us so long.

Got to security after - separated from sister in law who had our suitcase since her carry-on is too heavy to carry and she uses our rolling carry-on. Got through anyway in 10 minutes and on our way to Gate 49 - I swear it was a mile away, several escalators later, rushing almost running to the gate, where they were boarding our Group 2.

Learned a few lessons that day - allow 3 hours and confirm terminals.

I have a general rule of thumb.
3 hours - Long intercontinental flight from a big, busy airport
2.5 hours - Long intercontinental flight from an efficient airport
1.5 hours - Domestic flights with checked baggage
1 hour - Domestic flight with carry-on only
However, always check your airlines conditions.

Thank you, Nigel, Rachel, phred, Gail and djp_syd. Based on your info we'll allow 3 hours at LHR--we appreciate the check thru details. Each of your efforts really helped for our tomorrow!

My rule of thumb--3hours prior to scheduled departure for any flight. Sipping a coffee and using the airport W I F I watching late arrivals race down towards the gates is a way to pass the time. Lots of things can happen on your way to an airport and most of them are bad. Go early. Why risk missing your plane?

Follow up to check in at Heathrow, London
Terminal 2 (brand new facility) check in for United flight London to SFO, October 1st. Followed Forum suggestions, arrived over 3 hours early at about 6:45am--had pre boarding pass which would not function at check in station scan--there were few people in the check in line--there were personnel at each point to assist us with the check in, and with limited numbers checking in early in the morning it was very swift--our total check in from entry into 1st station to clearing security and into internal airport was under 15 minutes--Key was the few pre-boarding travelers at that hour--Thank-you for the advice from our posters, and we were happy to be early and people watch--
Caution and be time aware, if you are planning on a continuing flight in San Francisco: Our arrival and transfer at SFO was the complete opposite experience from London--At the same time, 2 large international aircraft passenger groups arrived into SFO security & customs, to go through the following: 1. self help automated machines for US passport holders checking your own passports & take your own photos. 2. Second station with officer passport check, had only 4 officers for combined US and other passports. It was a very large group. At this station aalmost everyone was required to do a machine scan of 4 fingers then the thumb. It took some people multiple minutes to clear, 3. fortunately we checked our bags and missed a long claim line then customs check 4. To move onto a continuing USA flight we were routed outside of the secure area, them had to re-enter the security procedure for the domestic SFO flights. Please laugh from here on: The re-entry was interesting. Being unaware security re- entry I left our London flight with a partially filled water bottle causing the scan line to halt (There was no spot on the controlled route, and no rest room access on our control route to empty bottle) Security lead me to a street exit door & said come back with an empty bottle and re- enter the security line. Going back thru the security scan line there were no containers to place anything in except for small key wallet ones. I put my money belt on the top of my day pack onto the rollers it fell off--called that to the attention of the security crew and they said there was no money belt with my passport-- which then lead to another line stoppage while they looked on the floor and found it. We were over 1 1/2 hours from stepping off our United 747, to being cleared into SFO. domestic flight area--Please keep laughing, now a five more hour layover for our connecting United express flight and all good, now boarding United Express for home, people lined up and on runway apron to load. Stop go back into terminal. No pilot. Stop, wait load the plane. Crew is there except the pilot. Keep laughing, and another hour and he arrives from being stuck in traffic. It was a great European tour and we had a lot of fun filled moments. Happy traveling to all of you

Oh my word Andy! What a time you had. Good Grief. This is good experience and fortunately you had a long layover!

I just came thru SLC on Tuesday but it was not as bad except for exiting out of the secure area and going back in with everyone else. The gal in front of me, the one behind me and I all had partial water bottles which we wound up chugging down as we got closer to the head of the line. No one wanted to chance a long wait having drunk a bunch of water, lol!!

Glad you had fun on your vacation!