If you need to dial the US from London, the short version is simple:
from a UK landline, dial 00 1 and then the full 10-digit US number
from a UK mobile, dial +1 and then the full 10-digit US number
That is the core format.
Where people get tripped up is everything around it: whether to keep a leading 1, whether US mobile numbers need a different prefix, whether an 800 number is actually free from the UK, and why some calls fail even when the format looks right.
This guide covers the practical version, not just the code list.
Quick answer
To call the United States from London:
Landline:00 1 area-code local-number
Mobile:+1 area-code local-number
Example:
00 1 212 555 0123
+1 212 555 0123
The US uses country code +1 as part of the North American Numbering Plan. NANPA explains that NANP numbers are 10-digit numbers made up of a 3-digit area code and a 7-digit local number.
Correct dialing format
If you are calling from a London landline
Use:
00 + 1 + 10-digit US number
So if the US number is 212-555-0123, dial:
00 1 212 555 0123
If you are calling from a London mobile
Use:
+1 + 10-digit US number
So the same number becomes:
+1 212 555 0123
On most phones, you enter + by pressing and holding 0.
If the number is already saved with +1
Just call it as saved.
You do not need to replace +1 manually if your mobile contact is already stored in international format.
Example numbers
Here are a few realistic examples.
New York
local US format: (212) 555-0123
from London landline: 00 1 212 555 0123
from London mobile: +1 212 555 0123
Los Angeles
local US format: (213) 555-0188
from London landline: 00 1 213 555 0188
from London mobile: +1 213 555 0188
Miami mobile or landline
local US format: (305) 555-0147
from London landline: 00 1 305 555 0147
from London mobile: +1 305 555 0147
If the number is shown domestically as 1-xxx-xxx-xxxx
Many US numbers are written with a leading domestic 1, like 1-332-555-0123.
From London, you still dial the international access plus the US country code and then the 10-digit number. In practice that becomes:
00 1 332 555 0123
+1 332 555 0123
If you see a number already written as +1 ..., that is usually the cleanest version to follow.
Landline vs mobile differences
This is one of the most useful things to know: the US does not use a separate mobile prefix in the way some other countries do.
That means:
US landlines and mobiles both use the same +1 + area code + 7-digit number structure
you do not add a special mobile digit when calling from London
the area code tells you the region, not whether the number is mobile or fixed-line
So the dialing format is the same either way.
The bigger difference is on the UK side:
landlines usually use 00 1 ...
mobiles usually use +1 ...
Also note one practical edge case: some hotel, office, or PBX systems in London require an outside-line prefix such as 9 before the international sequence. If a call fails from a hotel room or office desk phone, this is worth checking.
Cheapest ways to call the US from London
The dialing format is only half the problem. The other half is cost.
1. App-to-app calling
If both sides already use the same internet app and both are online, app-to-app calling can be free.
This works best for:
family or friends
planned calls
people who are comfortable using the same app
It works poorly when:
you need to call a real US landline
you are calling a business, clinic, hotel, or office
the other person is not online
2. Google Voice if you already have it set up correctly
Google Voice can be low-cost for international calls, but Google’s own help pages note two practical limits:
calls outside the US may use minutes from your mobile phone plan
if the call is not routed through Google Voice, your mobile carrier may still charge you
That makes Google Voice a stronger fit for people already inside the Google Voice setup than for someone in London who just wants the simplest path.
3. Browser-based pay-as-you-go calling
If you want to call a real US number from London without another monthly plan, browser-based pay-as-you-go calling is often the cleanest option.
When calling international numbers, people sometimes mix UK domestic habits into the sequence. For the US, you do not add a UK-style leading zero to the US number.
Treating the US like a country with separate mobile prefixes
US mobiles and landlines use the same +1 structure. There is no extra mobile digit to insert.
Calling a US toll-free number and assuming it will be free
This catches people all the time.
A US 800, 888, 877, 866, 855, 844, or 833 number is toll-free inside the North American toll-free system. It is not automatically free when called from London, and some may not connect at all from overseas.
Ignoring the time zone spread inside the US
The US is not one time zone.
From London, the timing can differ a lot depending on where you are calling:
New York and East Coast offices are usually 5 hours behind London
Chicago is usually 6 hours behind
Denver is usually 7 hours behind
Los Angeles is usually 8 hours behind
There are also short weeks each year when UK and US daylight saving changes do not line up perfectly, so the difference can temporarily shift by an hour.
Forgetting extensions
If you are calling a US office with an extension, dial the main number first and then enter the extension when prompted.
Why calls may fail
If your London-to-US call does not go through, the problem is often one of these:
the number format is wrong
the area code is missing
your line does not allow international calling
you are trying to reach a US toll-free number from outside North America
your carrier or app is routing the call incorrectly
you have weak data or Wi-Fi quality if using internet calling
If you are in London and need to call a real US phone number, BubblyPhone is built for the most practical version of the problem:
you do not want another monthly subscription
you want to call a US mobile or landline, not just another app user
you want to use browser-based calling over Wi-Fi or data
That matters most for uneven usage. If you call the US heavily one month and barely at all the next, BubblyPhone’s credit-based model is a better fit than subscription tools that keep charging the same monthly amount. You top up credit when you need it, and your credit does not expire.
Dial 00 1 and then the full 10-digit US number from a landline, or +1 and the full 10-digit US number from a mobile.
Do I need a different format for US mobile numbers?
No. US mobiles and landlines use the same +1 + area code + number structure.
Is it 001 or +1 when calling the US from London?
Both can be correct depending on the device. 001 is the practical landline version. +1 is the practical mobile version.
Are US 800 numbers free from London?
Not necessarily. US toll-free numbers are not automatically free from the UK, and some may not connect from overseas.
Why did my call to the US connect at the wrong price?
If your app or service did not route the call the way you expected, your carrier may have billed it as a normal international call. Google Voice’s own help pages warn about this if the call is not routed through Voice.
Can I call the US from London without a phone plan add-on?
Yes. Browser-based or app-based calling over Wi-Fi or data is often the easiest way to avoid buying a separate international calling subscription.
Final take
Dialing the US from London is straightforward once you reduce it to one rule: 00 1 from a landline, or +1 from a mobile, followed by the full 10-digit US number.
The real mistakes happen after that. People overcomplicate US mobile formatting, assume toll-free numbers will behave the same from the UK, or forget that carrier pricing can undo a “cheap” call if the route is wrong.
For most people in London, the best outcome is not just dialing correctly. It is dialing correctly and using the lowest-friction, pay-as-you-go way to reach a real US number.
