One ball is enough for approx 150 cm.

Finished size: approx 17 cm x 150 cm.

I have made a vest from this pattern.
Pattern name: Rectangle and square vest with collar by Avril.
See last picture

To read the chart:
Begin with 1 selvedge st, work 9 sts from chart, then rep the 6 sts (red box) 4 times, now you have 8 sts left, work the last 7 sts from chart and then 1 selvedge st.

The empty box means = knit stitch on RS, knit stitch on WS