For a ghostwriter, there’s nothing more exciting than that first conversation with a new client. We’ll talk about what they want their book to achieve for them, who it’s aimed at, and what they want to say.

But one of the questions that comes up time and again at this stage is, ‘How long should my book be?’

At first I was surprised this was so much on my authors’ minds, but I shouldn’t have been. We all need to have a sense of the size of the finished project when we start something, don’t we? It’s also a good question, because the length of the book has a lot to do with its goals, as you’ll see in a moment.

The easy (and most correct) answer is, of course, that your book should be as long as it needs to be. There’s no point padding out what could be a concise and punchy guide just for the sake of making it more wordy. Equally, if you’ve got a huge amount to pack in, then your book should expand to fit.

The beauty of business book writing – especially since the growth of e-readers and self-publishing – is that it’s a relatively new field. The rules are continually evolving, so there’s no need for you to feel constrained by some unwritten law that says your book needs to be of a certain length. If there’s a book you admire, why not count the pages, tot up the words on an average page, and see how long it is in total? That will give you a good guide if you want to emulate it.

Having said all that, there are a number of conventions regarding word count. It’s wise to be aware of these, as your book’s length will be one of the many things potential readers will take into account when they decide whether or not to buy. Of course, when books are bought online or downloaded onto Kindle this is less of an issue, but in some ways that makes it even more important to be aware of your readers’ expectations so they’re not taken by surprise when they actually start to read your book.

So what are these conventions? They depend on various factors.

Your readers’ expectations

The standard business book is around 50-60,000 words – although there are some who would say it should be more (and a few that it should be less).

There is a trend, however, for business books to be shorter. Time-pressed business owners would often rather choose a book they can read on a long flight, than spend hours reading in their own time. This means a 30-40,000 word business book is becoming more acceptable.

Memoirs, on the other hand, tend to be longer; readers are more predisposed to lengthen their attention spans for a gripping story.

The format

If you’re not planning on printing your book, but only making it available for e-readers, then your book can be shorter still. On a device, books are a bit easier to read when they’re less lengthy as you can’t ‘see’ the whole book in the same way you do when you’re reading a printed book.

The size of the topic

This has a big impact on the length of your book. If you want to write about a relatively narrow topic, such as social media advertising for example, your book can be relatively short. It may even be an e-book only (not printed) and designed as a reference tool for busy business people.

Remember … much of what you put in, you’ll take out

If you’re working with a ghostwriter, they’ll give you a steer on whether the amount of information you give them is enough (or too much) for your book. They’re experts in estimating how many words are needed to fulfil both your and your readers’ expectations.

If you’re writing your book yourself, though, it can be easy to get fixated by how many words you’re bashing out, and that’s great if it motivates you to keep going. But it’s also worth bearing in mind that – sad to say – a good editing process will take out many of the words you worked so hard to put in. Our words are always clearer and more persuasive for being pruned in the final edit.

Finally, I’ve talked in word counts here rather than pages, as the number of pages is influenced by diagrams, layout, font size and so on. And obviously for an e-reader it doesn’t make much sense to talk about page numbers in any case. But if it helps, you can assume that a printed book has around 250 words on a page.

I hope you’re feeling clearer on your book length now. There are no iron-clad rules, just some simple guidelines, of which you can make what you will. Your main aim is to write about the right topic, to the right audience, in the right amount of detail for them to take the action you want.