Is not a number. Its a sound, its a feeling, its a machanical sympathy. And it varies according to the car and engine type. Large engined cars, especially diesels can pull away at little over tickover. Small light-weight petrol cars can use a lot more. And for normal driving its not a case of dial up the revs and then work on the clutch, it's a subtle balance between accelerator and clutch.
And conditions too. Pulling gently away on the flat should barely raise a murmur, while pulling briskly away on an uphill start will need a different balance. And whenever you get into a different car there'll always be a brief learning curve of the accelerator /clutch balance, the clutch bite point and the sharpness of the brakes. The more practice you've had then the quicker you adapt to new conditions.