What is the maximum number of characters in an SMS text message?

Every mobile mobile phone in the world that has ever been made can send and receive SMS text messages. 

In 2020, 23 billion P2P text messages were sent every day, worldwide. 

Despite being incredibly clunky and basic, SMS clings on as one of the most popular ways for us to communicate.

If a message absolutely has to be received and read, then SMS is usually our messaging ‘app’ of choice.

But how long can a text message be? Is there any upper limit on the length of an SMS and if there is, why?

This arguably (definitely) dull post reveals all.

Maximum text message length

The maximum number of characters for a text message is 160 characters, including spaces.

This has been a global standard ever since the message was sent by a Vodafone engineer in December 1992.

You can of course send texts that are way longer than 160 characters but these are composed of multiple texts that are received seamlessly onto the recipient’s phone.

If you’re sending a message from one person to another, there’s no real maximum that you’re likely to come up against.

Most people in the UK are on mobile phone tariffs with very generous free SMS allowances, so it doesn’t really matter if a message than you send uses 1 text or 10.

The message length might be more of an issue for mobile phone users with pay as you go tariffs. If a standard text of 160 characters costs 11 pence, then it’s easy to see how expenses can quite quickly mount up.

Longer text messages are sometimes referred to as concatenated SMS

What’s the maximum length of text message that you can send using an SMS API?

The maximum number of characters that you can send in one transactional text using an SMS API is normally1280 characters. 

It varies for different SMS API providers so you’ll need to get the technical specification of the SMS company you’re using.

The following table compares maximum SMS message length from some of the main business SMS suppliers.

How is message length calculated?

When you’re sending messages of over 160 characters, each additional text has a character count of just 153 characters. 

The remaining 7 characters are used as code to instruct the mobile handset to stitch the messages back together, so that they arrive as a single, long text rather than a series of individual messages.

If the message that you are sending uses any non-standard unicode characters then the maximum message length is reduced to the just 70 characters.

Unicode characters allow you to send messages in other language scripts and also lets you send emojis.

Does sending a longer message cost more with an SMS API?

Yes it does.

The longer the text, the more text credits will be used to send the message.

The first 160 characters will use one text credit, then subsequent blocks 153 characters will use additional credits. 

The 7 character difference is used as code to allow the messages to arrive as one text, rather than a series of individual messages.

If you’d like to compare SMS API prices, take a look at our review of some of the main SMS API providers

Check your message with our free SMS length calculator

To help keep your messages under 160 characters and to see how many text credits will be required to send your A2P message, we developed a free and easy to use SMS message length calculator.

Simply copy and paste the message in to the window, the number of characters used will be displayed, along with the number of credits needed to send the message.

Of course other OTT messaging platforms like iMessage or Whatsapp have no restrictions on message length at all.

A well as calculating the length of your messages, you can also reduce them in length, so that they use fewer characters and reduce your SMS costs overall.

The SMS AI message optimiser uses ChatGPT to optimise messages that are just a little too long.

Related articles

What is concatenated SMS? Why use a simple word, when a complicated one will do. What is SMS concatenation? Find out here.

What is MSISDN? Another jargon busting article. This time we’re investigating MSISDN. It’s a roller coaster.

What the maximum length of a text message Is there a maximum? If so, what is it? Not a dull moment here at The SMS Works.