Use useful to say that something helps you do a job or solve a problem. It means it has value because it can help you in some way.
This tool is very useful for fixing bikes.
She gave me useful advice for my work.
Useful can describe something that has a specific purpose or role in science or technology. It means it works well for that role.
The machine has a useful output of 10 liters per hour.
Useful data is needed to complete the experiment.
Use useful to say that something can make things better or help you. It is good for improving or helping in a situation.
Exercise is useful for your health.
It is useful to learn new skills every day.
Useful can describe things or materials you can use to do something. They are not broken or wasted, so they help you complete a task.
The old parts are still useful for repairs.
We found useful materials to build a shelter.
Useful is used for knowledge or advice that you can apply in real life. It helps you do things better or understand how to do something.
He shared some useful tips for learning English.
This book gives useful information about cooking.
Sometimes people say 'useful' to mean the opposite, using a tone or context to show it is not helpful at all. This is an ironic use.
That advice was 'useful' – I doubt it will work.
His comment was useful, said no one ever.
