I have received a pack of resin and hardener,and the only mixing information is by weight.

As far as I know I think it is still easier to mix by weight :p might be personal.

As Matthieu said, most materials (especially liquids) change volume with temperature, the resin and hardener may change volume at different rates so your mix ratio would be different at 17deg and 25deg. Maybe only marginal but ratio by weight is more accurate and will not change the ratio if working in different temperatures

Get yourself some syringes. Makes measuring by weight an absolute breeze. I used to be happy if I could pour within 0.05 of a gram of what I was aiming for, but with a syringe I can get it spot on to 0.01 of a gram every time.

Use the data sheet density data to convert from weight mixing ratio to a volume one.  We don't recommend it generally as epoxies are sensitive to accurate mixing ratios and it's introducing another potential area of error.

You can get micro scales that will go down to really tiny weights if needed.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant