Hi @Morton seems to be is possible: https://stackoverflow.com/questions/31265388/spree-prices-based-on-weight

Thanks @Enrique Meza, I have seen the variants used before. The problem I have is the price is per kilogram. So a transaction of 1.67kg is not easy to create using variants. I have tried to create a price per 1gram but the pricing can't usually go past two decimal places.

Ok got it, that was I did (price per 1gram) long time ago with my point of sale :http://donmanolo2.sourceforge.net/