That is no real indicative weight technique as weight distribution, unconscious bias, distractions etc can easily skew such an estimate. Also if you're strong enough to lift 10kg then lifting 9kg won't feel much different.
These are some of the reasons why scales exist. Bb
My surname is Salter and I am a set of human scales.
Just found a review on tredz that said 19lbs/8.6kg - they didn't specify exact height above sea level and the ambient temperature at the time of measurement so I'm sure it is wildly inaccurate.
Seriously though lifted it compared to my 10kg bike and it felt about 1kg lighter - if that information is useful great; if not please ignore - that is the reason forums exist.