I say that I am 99.99999...% atheist not because I think a god might exist, but because I acknowledge that I simply cannot know with 100% certainty that no being that we would call a god exists. I am, however, 100% certain that the god of the Bible does not exist. I can find evidence of this in the Bible itself. And, as for other man made gods, I am certain that they are also, well--man made.

I also like to use the 99.9999999... percent. Yet, if there is a god I also like what Mark Twain has said of it: "If there is a god, he is a malign thug."

I am with Joanne, in that I am 100% sure that the judeo-christian/moslem god does not exist, but only 99.99999% that there is no other god/gods.

I think mankind gets so wrapped up in nomenclature that even the broadest of topics can often become narrow and categorical.
Spirituality = God
Universal frequencies= God
Cosmic energy= God
OR
Dog = God ......hehehe

'Why do you say that you're only 99.9% sure that god doesn't exist?'

Because if I don't hold back a tiny bit of self skepticism I might shut out some evidence of a god or gods that may exist which I've overlooked. I don't want to be 100% certain of anything because I might be mistaken about it.

'I'm not currently in my garage, but I can say with 100% certainty that there is not a full size African elephant wearing a pink tutu and dancing the macarena in there (you're welcome for the visual).'

if you're not there how can you be 100% sure? Maybe there IS (perhaps!)

'But unlike god, we can prove that African elephants and tutu's exist.'

And maybe both are in your garage right now (perhaps!)

I say 99.9% because of one simple reason: you can't prove a negative. No one has ever proven even a remote chance of a god existing and I'll bet anything they never will but just like religious people can't know for sure non believers can't know for sure a god doesn't.

While I will be very, very, surprised if God turns out to exist (and I will be aware of this) I can not say 100% of anything that I believe will ultimately be true. I am fond of saying that there is nothing written which can't happen.

I accept as fact that there is something, somewhere, somehow, that has caused me to be here... if indeed I am here... at this place and this time. Maybe a star fart, a faulty atom, a quark spark, a grain of space dust, Mother Nature, whatever there was a causation, and this "something/that causation" could be a "god." However, from what I know of history and of the history of the Bible, there is no way I could accept as fact that God, Jehovah, Yahweh. Heavenly Father as described in the Bible ever existed except in the mind of men who wrote down stories they created or had been told.

I can demonstrably show that there is no elephant in the garage, because I can see the whole garage at once. We can’t prove that something doesn’t exist anywhere in the universe because we can’t perceive the whole universe. Given current evidence, both gods and aliens seem to be creations of human imagination.
But I believe that is highly probable that there is life elsewhere in the universe - it’s a big universe! I believe that it’s more likely that there is alien life than that there is a being that created everything else. But as of now, neither of those things can be “proven” to exist or not. So I can only be 99.9-something % sure that there is no god.

I say that I'm 99.9% sure because although I have never come across any evidence that any gods exist and I've seen plenty of evidence that no benevolent gods exist I also realize that the universe and all of reality is vastly larger than my comprehension and I cannot absolutely prove that a god-like entity does not exist. The likelihood of gods existing is so small that I give it no real thought. Its more an admission that I don't know everything.

Also, elephants cannot do the macarena. But, you could not be 100% sure there is not a baby elephant wearing an extra-extra-extra large pink tutu standing in your garage listening to The Macarena song.

I didn't answer that question. I think that anyone who claims to know something that is unknowable, should not be trusted.

As for all the percentages between 0% and 100%: how would someone measure their certainty with any kind of accuracy? How would you account for possible evidence you've never seen? How would you account for the simple fact that it's impossible to prove a negative? Picking any percentage would mean you pick a totally arbitrary number. It's meaningless.

Why can't I just answer, "I don't know"?

By making the claim that I am 100% certain there is no god, I'm taking on the burden of proof to support my claim.

I can't very well tell a theist who is 100% certain there is a god that I need empirical evidence to support their claim if I can't support mine.

By saying i'm 99.9% certain, I can reject their god claim without having to prove a negative.

I said something like 99.9999999%. But here's another take on it. I'm 100% certain the Judeo Christian god described in the Bible does not exist, but there is a non-zero probability that some beings who are much more advanced than we are are exerting control on our lives. We are the most advanced beings on Planet earth, but we're only about 50,000,000 years more advanced than mice. It would be easy to design a scenario where one of could control a mouse for his entire life, and keep him completely in the dark about whether we exist or not. The Universe is 14,000,000,000+ years old, so there is a nonzero probability that other beings out there are 50,000,000 years farther along than we are in intellectual evolution. Those beings could be controlling us without our knowledge.

I don't say 100% because it is so frustrating to theists to hear a non believer say "I don't know for certain" or "I could be wrong" because they arrogantly assert that not only they are not wrong but that they can't be wrong and when confronted with arguments that point out the flaws in their logic while at the same time admitting that there is a chance - no matter how small - that we could be wrong it presents a level of intellectual honesty that exposes their levels of intellectual dishonesty in a great way.

I'm aware that my knowledge is limited. That said, nothing that I had experience and learn points toward the existence of such entities, hence the 99.99%.

So uncommon, and yet freedom from religion needs a healthy dose of common sense and a bit of courage!

I don't know. 100% didn't feel right.

well its good you brought up an ontology example

There should always be that .01% for doubt. Being skeptical is always a good thing and that .01% allows us to be skeptical of our own skepticism. And it's important to keep that .01% of an open mind to things we don't understand scientifically, yet. Let me quote from a great mind:
"There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy."
I come from a family of lucid dreamers. My brother who was Mr. Stoic-the-Science-guy-100%- atheist came to breakfast one morning, and actually talked about a dream he had, the only time he ever talked about a dream. EVER. He said it was so real it scared him. He said that a masked man had plunged a knife into this chest and cut him all the way down to his pelvis. The next day my brother was in surgery; he was cut from his chest to his pelvic area. He was tackled so hard playing football that he had ruptured organs. How is that to be explained? We need room for doubt.

Really? The tutu wearing, macarena dancing elephant doesn't exist? I guess scientists say 99.9% because we have to give the bible thumpers that .1% chance so they can still hope. I mean, hope and faith, right? That's what they're all about.

Because it is possible we're in a simulated reality + arguments for non-conscious deities. It is like the gravity is a theory but put into practice there is almost certainty that you would fall off that building and die if you jumped.

Because of the sheer magnitude of the universe and our lack of understanding of it, there's always a chance.

I'm 99.9% sure that it's not raining fire at the moment. But, if I don't look out the window to check, there is always a slim possibility that I'm wrong.

I chose 99.9% because I thought it was funny. I work for a DNA paternity company and that is what we have to use. Its basically a 100%, but legally we can't say that because we would have to test every man walking the planet and of coarse that's impossible. Plus on the scientific side of it, nothing can be 100% . You can get as high as 99.99999% but there will always be .01% margin of error. That's kinda how I feel about there being no god. Sorry my nerd came out, lol.

I guess I look at it as I can only believe or not believe in gods that have been proposed. I can't believe in a 0.00000000000001% chance that some hypothetical god that has not yet been proposed can exist. I personally take the null approach for any god that has not yet been proposed; so it can not fit into the equation of whether or not a god exists. If the skies part tomorrow and something claiming that it is god appears tomorrow, I'll re-evaluate.