What should the blast size of a 75,000 square foot cube of platinum be, give or take a few feet? The damage is 3,645d8.

Edit: Forgot to mention that it's falling from the edge of space.

There is no official way of calculating this effect.  Your best choice would probably be to say the blast radius is 40 feet - that is the impact radius of a single meteor from Meteor Swarm, the closest analogue to an object falling from space.

There are some other things you could do - you could do equivalency calculations using the in-game rules for dynamite or perform some physics calculations based on density and impact.

I am curious how you came up with your damage calculation.  I am sure you did something to calculate that specific number, but would want to know what. Explaining your math for the 3,645d8 figure might provide clues on how to calculate a blast radius in a manner consistent with your other calculations. 

2 questions, how did you get that much platinum and how is it in space. Actually 3 questions, next is why?

Quote from BIackBear >>

2 questions, how did you get that much platinum and how is it in space. Actually 3 questions, next is why?

 I was going to ask the velocity.

Quote from DaOtterPrinx >>

Quote from BIackBear >>

2 questions, how did you get that much platinum and how is it in space. Actually 3 questions, next is why?

 I was going to ask the velocity.

 Falling? So terminal velocity? Does that even apply in space?

Quote from DaOtterPrinx >>

Quote from DaOtterPrinx >>

Quote from BIackBear >>

2 questions, how did you get that much platinum and how is it in space. Actually 3 questions, next is why?

 I was going to ask the velocity.

 Falling? So terminal velocity? Does that even apply in space?

 It’s just the edge of space, so it slowly starts getting pulled back down.

But what’s it’s velocity when it hits?

Because then we can calculate the blast

Also I believe it would be cubic feet, not square feet, otherwise the impact would have no effect.

Jeez this thing weighs 100,533,750lbs

Quote from ZeusTheGreat173 >>

Also I believe it would be cubic feet, not square feet, otherwise the impact would have no effect.

 I was thinking that...

Quote from ZeusTheGreat173 >>

it would weigh quite a lot

there are also terminal velocity calculators you could check

 But does that only apply on earth’s gravity? Also, how can things fall? It’s space!

Edit, it does not, we can’t calculate without the velocity.

Quote from DaOtterPrinx >>

Quote from ZeusTheGreat173 >>

it would weigh quite a lot

there are also terminal velocity calculators you could check

 But does that only apply on earth’s gravity? Also, how can things fall? It’s space!

Edit, it does not, we can’t calculate without the velocity.

 It’s just at the edge of space, so gravity still slowly draws it into the atmosphere.

And what is the exact duration and distance of impact

Quote from DaOtterPrinx >>

And what is the exact duration and distance of impact

 distance is about 434 miles i believe

Terminal velocity is 1906.4259 ft/s

Whats the duration then?

Quote from DaOtterPrinx >>

Whats the duration then?

 uhhh the speed increases by 9.8 meters per second

Quote from ZeusTheGreat173 >>

Quote from DaOtterPrinx >>

Whats the duration then?

 uhhh the speed increases by 9.8 meters per second

 until it reaches terminal velocity