Look up the median monthly pay for a salaried position that does the same job. Then divide by 22 days and then how many working hours per day mandated in your country. That is the cost per hour.
To quote for a project, you must factor in materials cost, travel, food, accomodation, petrol, parking, mileage, etc etc in addition to the labor charge. And then you multiply by the % profit margin. All of these varies greatly depending on your local market prices. This means you have to do some market surveys a.k.a. buttering possible clients and asking them what they paid for similar services.
If you're a newcomer, put in a bid that is only slightly below the market price. DO NOT put in a very low bid as it wil actually turn away potential clients since they are wary of your work quality or if it got accepted, you won't make a profit. It sucks but you will need to take several projects before you get a feel for pricing.
BUT, freelancers or ahem, CONSULTANTS are the modern day soothsayers and mendicants of babby CEOs. We get paid a lot more to say and do the same things that in house staff have been desperately trying to get approval for, without having to deal being a wageslave. Use this knowledge shrewdly to jack up your price once you have gained around 5 years of experience.
P.s. register for a LLC or equivalent for your freelance business. It gives you an aura of credibility and simplifies your taxes while somewhat shielding you personally from lawsuits and bankruptcy.