After making the first gathered apron that turned out a bit to narrow I realised that I needed to make some comparative smocking to see how much fabric that was needed for the desired width.
I cut out four pieces of fabric all 30 cm wide. On three of the pieces I made gathering stitches 1 cm apart and on the last one I made the gathering stitches 1,5 cm apart. Then I made a simple honeycomb pattern on all four pieces with a 1 cm, 1,5 cm and 2 cm distance between the rows on the pieces with the narrower gathering stitches. On the piece with the gathering stitches 1,5 cm apart I made the rows 1,5 cm apart.
The bottom two became to narrow and the one on the bottom right had got a to deep pattern because of the gathering stitches being 1,5 cm apart. I like the two on the top and the one on the left is the one I’m using. After smocking it measure about 17 cm wide which means that I have to use twice the desired width of fabric. The other ones need at least three times the desired width of fabric which will make the bottom part of the apron to large.
This little comparative studie was really quick to make and I really recommend anyone to do it, if not just to practice smocking and ge a feeling of the final result.
Cristina's ramblings 
This brings up a good point about making a sample. I will have to remember it when I get around to making my own smocked apron (although it is way down on the list, alas…)
Thanks for posting this! I’ve also learned the hard way that I have to do a sampler first 🙂 I also prefer the top left one!