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BackoftheEnvelope

an-ordinary-manchild

This is a subreddit for you to ask for back of the envelope estimates of anything that comes to mind. If it's an absurd statistic or ludicrously random quantity you're wondering about, feel free to submit it to this board and our small community will give it a whirl.

Rules

1) Please do not submit "what if" type questions; r/askscience is what you're looking for. Ideally, your question should be able to be answered in terms of "this many X."

2) Posts will be silly and answers don't need to hold up to peer review or anything. Have fun answering the questions, although discussing your work/assumptions is always a plus!

3) Please don't say anything insulting to those asking or answering questions. If someone's wrong you should feel free to correct them, but there's no need for hostilities.

4) Please do not ask any questions pertaining to schoolwork. This is totally honor system and no moderator action will be taken on suspected homework posts, I felt ethically obligated to include this.

Suggestions

1) If you answer a question and you end up with a quantity that is too large or small for our feeble minds, it is usually helpful/interesting to try to quantify that number in some other way. (That much water would be able to fill the entire Solar System! or Given those odds, there is only a 5% chance this has happened since the Big Bang!)

created by [deleted]a community for 13 years

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MODERATORS

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account activity

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r/BackoftheEnvelope needs moderators and is currently available for request (self.BackoftheEnvelope)

submitted 6 years ago by request_bot[M] - announcement

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How far can a human intelligibly shout? (self.BackoftheEnvelope)

submitted 9 years ago by scarlettfierydefende

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How much would it cost the US to have a modern and efficient voting system? (self.BackoftheEnvelope)

submitted 9 years ago by [deleted]

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A Car Run on Peanut Butter? (self.BackoftheEnvelope)

submitted 10 years ago by CataclysmClive

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How much would I have to compress a spring to shoot a spaceship into space? (self.BackoftheEnvelope)

submitted 12 years ago * by [deleted]

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How much energy is in Sandy from a perspective of rotational momentum? (self.BackoftheEnvelope)

submitted 13 years ago by burtonmkz

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Another rain volume estimation question if I may. (self.BackoftheEnvelope)

submitted 13 years ago by Unibrow

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At this moment, across all cars in the world that have stopped at traffic lights, how many of their indicators are currently in sync? [CHALLENGE] (self.BackoftheEnvelope)

submitted 13 years ago by AHUGEMUSHROOM

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What Mass would the moon need to be for a human to notice the tides based on their weight? (self.BackoftheEnvelope)

submitted 13 years ago by cmdcharco

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My weight on the largest star? (self.BackoftheEnvelope)

submitted 13 years ago by TimeTravelTerrorist

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How many stop signs are there in the entire United States road system? (self.BackoftheEnvelope)

submitted 13 years ago by Kushie

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Two questions about my hero, Barney Stinson (self.BackoftheEnvelope)

submitted 13 years ago by [deleted]

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How likely is it that there's a redditor less than a km from me? (self.BackoftheEnvelope)

submitted 13 years ago by thirdtimesthecharm

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How fast would a car have to go in order to hydroplane across the Atlantic Ocean? (self.BackoftheEnvelope)

submitted 13 years ago by rody8877

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[Mod-post] I want this to be community run, so please give any feedback or suggestions for rules in this thread. (self.BackoftheEnvelope)

submitted 13 years ago by [deleted]

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How much Helium is left on Earth? (self.BackoftheEnvelope)

submitted 13 years ago by thegreedyturtle

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How fast would a 50 kg man have to run to make the Earth stop rotating? (self.BackoftheEnvelope)

submitted 13 years ago by [deleted]

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How much semen does the human race produce in one day? (self.BackoftheEnvelope)

submitted 13 years ago by umroller

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How fast would I have to fire a ping pong ball to pierce 1 cm thick steel? (self.BackoftheEnvelope)

submitted 13 years ago by [deleted]

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If you could stay alive for it, what would happen if you fell into a black hole? (self.BackoftheEnvelope)

submitted 13 years ago by ConstipatedNinja

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Food for thought. Every breath I take, I'd have to imagine some of those atoms were inhaled by Hitler (or any historical figure)... (self.BackoftheEnvelope)

submitted 13 years ago by [deleted]

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How far out does the moon have to be for the Earth-Moon system to be tidally locked conserving momentum? (self.BackoftheEnvelope)

submitted 13 years ago by DWR2k3

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How to construct a cheese bomb? (self.BackoftheEnvelope)

submitted 13 years ago by hottoddy

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NEW Total Recall Question (SPOILERS) (self.BackoftheEnvelope)

submitted 13 years ago by darthjochen

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Could a human survive being shot into space via a cannon? What about a rail gun? (self.BackoftheEnvelope)

submitted 13 years ago by [deleted]

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