How to work out petrol cost for new job

[DC_FC]

Basically im looking for another job and theres 1 ive seen but its twice the distance i currently do eg
at the moment i drive 14.7 miles 1 way and this job ive seen is 29.3 miles 1 way. My question is is it possible for me to work out how much petrol would cost driving to the job thats 29 miles away, is it just a a simple case of top up with petrol at start of the week then when it gets to friday top up with petrol and note down the mileage, am i on the right track or not

thanks

[DC_FC]

Just to add ive worked out my mpg so i can use that if need be

[sigma]

Simply doubling your fuel cost will only work if both routes use the same type of road, ie. both urban or both dual carriage way etc.

[DC_FC]

I spoke to soon as they got back to me and said no thanks,

thanks b0l10x yes if its double the distance then it woudl be double petrol cost but as sigma states it depends on the road well at teh minute half of the roads i use at the minute are crap but from past experience the roads i would have used to get to the job i was applying for are much better