First of all under different circumstances you either charge in an hourly rate or a flat rate, whichever is most convenient to you.
Depending if the project or work is requires more time, charging by the hour is the more appropriate approach to you. In addition, if you think that the work will need refining or more time on it to make it perfect more hours means more money in your pocket. To come up with a number first there are multiple elements that go into the creation of a price. First what the project is if its for a web design, app design, brand design, or print design. Who the client is, if its a small private employer or a prodigious corporate business. The final key for hourly rate is how much time it would take of your time working on the project. With all the elements into consideration whether your employer is someone paying out of pocket or a large corporation. You have to take into consideration how much time this will actually cost yourself in time, when you can easily be doing something else. Ranging from a private employer, a lesser price per hour will be necessary because the employer wouldn’t have too much to give if its a small business, and charging a smaller amount say 70$ per hour would be relatively an OK price. If the employer is outstanded by the reasonable numbers you give them, then you have to charge more, when they want to negotiate the price is when your price is either right or a little too high. Hourly charging rates are more efficient than a flat rate if the project is bigger than average and if you’re putting more hours to refine, and perfecting the art its best to have hourly rates. Having 400 hour payday or whatever your rate is, will equal an amazing payday. For hourly rate calculations its best to use this website as it takes in consideration all key elements that were talked about.
A flat charge is recommended for a work or project that wouldn’t necessarily take as long as an hourly job would take you. For example you and another graphic designer are hired of equal skill but different working rate to do the same job but in a similar but different way. You take 7 hours to make the logo or whatever the design job may be and the other took 13 hours to make it and are both payed 100$ per hour, so you make 700$ while the other person made 1300$. To avoid any gap you would charge a flat charge of 1000$- 1300$ depending on how you value your hours. In addition, the same thing goes for flat rate in taking consideration of who is giving you the job, if a big corporation is employing you, you want to charge more because of the amount of money they have. Wanting more accordingly to what job it is and how much time it would take you. Also, after working for them you have to come up with a price for them to take your work and reproduce your graphic design(hopefully a large amount of money) more in depth numbers and elements can be found here to come up with a reasonable number.