"one million kilograms" = one gigagram
"4.3-billion-kilogram" = 4.3 teragram
"tens of thousands of kilometres" = tens of megametres.
I don't understand the media's reluctance to use large SI prefixes for mass and distance, when they'll happily use them for electrical units.
Only place where I've witnessed it's use is during my own personal musings while sitting on the loo. Same goes for money. "Gigadollars" has a nice ring to it but it's not used :(
There are other units of measurement when the numbers get really big, like AU, lightsecond/minute/year, Solar Mass, etc. I'm no scientist, but I also think when you get to the astonomical scale, order-of-magnitude relative measurements is more useful knowing a galaxy's mass to the nearest gram.
Case in point, people might think you are conflating nuclear bombs and mass if you say "this ship weighs 5 megatons".
Also depending on who you ask, gigagram either sounds like way more, or way less, than 1000 tons.
And for scientific writing, 1e9g is about as clear and explicit as it gets.
Thus it's normal to use e.g. 1e6 kg rather than 1e9 g.
OTOH, 1KHz has no basis in physical reality for normal people but they know 1KHz is 1000x faster than 1MHz so it works nicely for things like "is my new computer faster than my old computer" (at least a decade ago, I don't see clocks advertised much at all anymore).
It stops on the ton, though - “40 thousand tons of grain” - gigagram isn’t used.
Re kHz, I think most people understand frequencies we can hear. (1 kHz is close to a high C note). MHz and GHz are radio frequencies.