Have just measured a dildo I bought from LH years back to see its circumference, it measures 6" around. I have been using it today (anally) while masturbating.
I just went in the bath and saw a clear plastic bottle of still water my wife had left on the side, its one of those that has a rounded bumpy bottom. The circumference much more than the dildo.
I toyed with it and used some lube. I couldn’t get it in while laying in Bath, (lube washed away too) I even tried the dildo first to loosen things up. In the end I got out of the bath and knelt on a towel on the bathroom floor with the top of the plastic bottle against the floor. In this kneeling position I sat on it and pushed myself down. I found wiggling my bum from side to side was helping it push in. It was difficult but I had to carry on, changing angles while I went it finally slid in and omg! What a incredible feeling. So tightly in there though so I sat up a bit then gently thrusted it in and out. Omg, so so good.
I’ve edged myself and will finish off later (hopefully in wife) I was Interested to know what I’d managed to take so I measured to find it was 8.5" circumference. I know I couldn’t take anymore … that is maxed out lol and anymore my bone structure would not allow.
I’m looking now at getting an 8.5" circumference dlldo or butt plug from LH.
It would be good to hear what circumference is deemed as big, normal or possible and what others have found or done?
My biggest plug is 7.5" circumference and, at the moment that’s the maximum I can take (mind you I’ve said that before).
Thank for this… I guess I could be seen as pretty experienced in the anal play scene then. The max I’d done before was 8.25. A 330ml drinks can is 8.25 but I won’t say how I know that lol!
The thing with the bottle is it pretty solid. Plugs and dildos have a little give so can squash a little into a more accommodating oval if that makes sense. It mainly between the butt cheeks just cannot get anymore width so will be stopping at 8.5. I did notice the ace of spades 
plug which I think is 10" circumference! How does that work? Certainly wouldn’t fit in me!
From my experience in buying toys the follow is basically who the sizes ar categorised
Small: 4.5” circumference and smaller(cat. normal)
Medium: 4.5” to 6.25” circumference(cat. normal
Large: 6.25” to 8.5” circumference(cat. possible)
X-Large: 8.5” and bigger (cat. Big)
And the biggest plug I can take is a little over 10” in circumference.
I could possibly get to 10" or over if I used two 5" circumference dildos - like longways between balls and top of bum crack if that makes sense? Is that cheating lol?
My butt plug is HUGE, the answer to your question( and I can testify) the maximum size is the space between your pelvis bones ( bigger for females) my butt plug is about 13" circumference
Wow! Yes I thought it would be different for girls as for obvious reasons there needs to be more space available in that area. 13" is quite something though.
Also thinking about it, it’s not clear if @beats69 is girl or man?
Your bum is a muscle trained over (quite) some time it can stretch a long way without issue though it’s look can change think watching videos of two hands there whether male or female
I am a male and love playing and stretching my ass with my buttplugs and dildos
Sorry 
i was just going to comment that ive seen some pretty massive fantasy dildoes used anally (strange things can get spat out of the internet when you go looking for fantasy toys). 10”+ circumference is pretty common for fantasy stuff and ive seen 15”+ on many dildoes. Ive seen some anal toys by fantasy makers that are 12” circumference. though whether that will be feasible or not is going to be down to anatomy.
Please be very, very careful about inserting anything without a flared base - like a water bottle. There is a good reason why all anal toys have those. You don’t want to end up in A&E trying to explain that one.
Oh boy, aren’t these circumferences over 10" just harmful? It’s pretty hard for me to imagine the anus returning back to the original shape after something like that. Even vaginal sex with girth that high will leave vagina very loose after some time. Could someone elaborate on consequences of something like that with anal?
I applaud your recycling efforts! 
A year ago I bought the Nexus Ace Large Extra Quiet Remote Control Vibrating Butt Plug 5 Inch, not quite realising just how big a 6.25 inch circumference is! First time I tried to use it I couldn’t even get the tip in, took me 6 months, lots of failed attempts and lots of lube. Now after using it a few times it goes in relatively easy as long as I’ve worked up to it and feel relaxed, it feels amazing! I highly recommend it to you, it has a great shape, will be much easier to insert than a plastic bottle, and most importantly it has a flared base so takes away the risk of having to visit A&E with a plastic bottle stuck up your bum 
I recently visited a sex shop that predominantly caters to gay men. Some of the stuff they had there would make your eyes water! I’m taking anal toys that bigger than the circumference of my head!
This is a concern of mine too. I mean at 8.5 circumference is as much as bone structure or pelvis will allow side-to-side. I could go bigger longways with a more ovaled shape but anus will probably begin to resemble a slit rather than a hole! Lol I think I could take two 6" round dildos in this way, but do fear of going over the top and causing permanent stretch does worry me. So, I think I may just buy max 8" circumference dildo so at least I can use it without the concentration and time taken to get it in.
I guess the old rule applies too, go easy, if it hurts don’t do it.
You’re right at the largest sizes oval shape would be better and yes the hole does end up like a slit as I can testify but done slowly, I’ve been playing for 35+ years back there it’s still all good
Never really measured what circumstances I’ve taken but isn’t it funny when see certain objects and think oh wonder what that’s like up the bum haha 
Great info thanks 