Measure the width of each window (front, sides and back) then make the each curtain three quarters of that length. When the two curtains meet half way there will be enough gathering in both of the curtains. This would give you the right amount of gathering in respect if the press studded tie backs as too much gathering will restrict clipping them back.
When you have added all the window widths together you will then have a total of how much material is required if that's what you mean about working out the meterage.
If you are anywhere near Liverpool or Newcastle-under-Lyme the One Price fabric shop sells all fabrics for either £4 or £5 a metre, not sure which at present. It's good quality for a fabulous price. If you've got the original curtains measure each of them. Most fabric is 137cm wide. Draw out a plan allowing about 3cm for each side hem, 3cm for the top and 7cm for the hem. You can then work out how many metres you need. You need to cut each curtain the same way up and if you've got a pattern you need to allow for pattern matching. Most caravan curtains are lined too.
------------- Jean
Sometimes a little rain must fall before you reach a rainbow.
The work will wait while you show the child the rainbow, but the rainbow won't wait while you finish the work.
Many moons ago when I was studying textiles, I used to work in a fabric shop at the weekends and the rule of thumb for good looking household curtains using a header tape rather than eyelets was that you should use 2.5 times as much fabric as the width of rail you want them to cover. This allows for really good gathers. However, I think this would be overkill in a caravan, especially as the windows are so small, so I would be tempted to use 1.5 or 2 times the width. It also might depend on your choice of fabric. Heavy or textured fabrics are more bulky and therefore too much width would give a very bulky finish whereas if you use quite a light fabric and you don’t have enough width, they may look a bit sparse!
Caravan curtains are only installed mainly for cosmetic reasons really just to make it more of a home from home luxury as most people close the sun blinds at night therefore the gathering isn't that critical so as long as the curtains meet in the middle with a bit of gathering that's all that matters. The important part is not to achieve too much gathering otherwise there will be problems with the wrap around tie backs.