Why book-to-bill matters to a first-time founder
The ratio sets new orders beside what you billed in the same period. Above 1, you are taking orders faster than you invoice them, so the backlog tends to grow. Below 1, invoicing is running ahead of new orders. That is a demand signal. It says nothing about whether the orders make money, or whether customers will cancel.
Examples of book-to-bill
A contract electronics firm in Suwon takes KRW 480 million of new orders in a quarter and invoices KRW 400 million. Book-to-bill is 1.2, so the order book is growing. A later quarter at 0.8 would mean invoices outpaced new orders, even if profit looked fine because older work was billed. The firm writes down what counts as an order, so a cancelled quote never enters the numerator.
Common misunderstanding
The ratio is not profit, not cash collected, and not revenue growth by itself. Billings are amounts invoiced. They can differ from cash received, and from the revenue you recognise, when the accounting rules time those events differently. Orders that customers can drop at will are a weaker signal than committed ones. The sales report has to use the same definitions every month.
When to use it
Use it when you take the order now and invoice later, as in manufacturing, components, or project work. Read it next to backlog and cancellations. A shop paid at the till on the same day learns little from the ratio that its daily sales do not already show.