What's sf? Square feet? Even though you've said you have 152 sm of garden? Hmm, I'm confused - check the box or pack of grass seed - it tells you on there how much you need per metre, and how much a pack will cover.

2 0unces per square yard, 6.25 grammes per square foot.

Great month for sowing lawn seed, I agree with Bamboo look on the box? I found with the different types of grass seed e.g. hard wearing the amount does seem to vary