Is this a boy or girls name?

It's not "probably" more common for boys-it's 10x more common for boys!

I think it can be both but probably more commonly used for boys. I actually taught a class with a male and female Ellis in it.

@marshallzumarubble So is there anything that defines a name as officially male/female/unisex? Or is it just left up to our own consideration? So taking Ellis, people saying ‘it’s a boys name’ are basically saying they consider it to be a boys name, just as some consider it unisex?

DD is called Ellis. It's not her registered name, but I've been calling her that for years.
I started watching Grey's Anatomy on Prime a few weeks ago and was really surprised to see a character called Ellis.
I once met a little girl called Ellis. She's about 10 years old now and it is her official name.

I know a female adult Ellis.

Marshall-that's really interesting-(although I did read entomologist at first, which confused me......)
Is there any evidence for what seems to be the fact that once a name reaches the point where it might be genuinely unisex, people stop using it for boys? Like Joscelyn and Hilary from days gone by?

It's a boys name. I've never heard a female Ellis but loads of male ones or rather Elis as am in Wales.
It's not a name I like for either.

I've known a few female ellises, I really think it's for either gender.

I actually thought girl first as it is feminine sounding.

Going off a little from the original OP but you asked so...

I'm an etymologist, specialising in names and naming practices.
We tend to consider a name unisex when it hits the 40:60 ratio. There are very few truly unisex names and they of course can change year on year and also, to a certain extent, in different generations. Consider the nickname Chris; in a person aged 40-65ish then it is absolutely unisex. I wouldn't know whether to expect a man or woman if told I was meeting Chris Jones for example. In a younger generation, say a person under the age of 20, I would expect a boy as, statistically Christopher has remained reasonably popular compared to Christine/Christina.

Generally unisex names tend to be shortenings or nicknames (Chris, Sam, Charlie for example) or surname names (Taylor, Morgan, Riley etc...).

And of course names move about as time moves on, there are lots of names that we previously considered male that have moved to unisex and then to female such as Tracy and Kelly. We are currently seeing this happen in the US with the name Riley. It was predominantly male, moved to unisex about 10 years ago and is now a lot more popular for girls than boys (25th in the American charts for girls, 253rd for boys).
Movement the other way, from girls to boys, is a lot more unusual.

“Thanks for educating us all!”

You’re welcome!

@BertrandRussell Oh so Frances is the only unisex name? So that’s it, we’ve all been told then. Thanks for educating us all!

There are no unisex names. Except I suppose Frances/is. There are boys names that people occasionally use for girls. And when they reach a tipping point, they become girls names which are no longer used for boys.

I went to school with a girl called Ellis, but over the years have met boys and girls with the name. I think it's one of the few that can be either.

I know more boys than girls but both spelt and pronounced the same

Ellis is a lovely name for a girl in my opinion! Elise is a completely different name not sure why it's even been mentioned...

I've never heard of it as a girls' name but I love it!

Unisex names, I think, are names commonly use me for both. Calling a girl, ‘James’ doesn’t make it unisex for example.

Ashley - 414th most used boys’ name
Ashley - 797 most used girls’ name
Ellis - 89th boys’
Ellis - 1105th girls’

So from the statistics I would say that Ashley is rarely used for either and Ellis almost never for a girl. I think I would question Ashley but never Ellis for that reason.

So at what point does a name become unisex? Is Ashley a boy or girls name? Or Unisex?

The only Ellis I've heard of is Ellis Grey from Greys anatomy and she's female so that's my association of that name

Giving a girl a boys’ name does not make it unisex. It’s exactly the same as calling a girl Dave only even fewer people have done that. Yet.

It really isn't a proper unisex name given that, looking at the statistics, in 2017 96% of Ellises born were male and 4% were female. This is generally the pattern on all the records since 2000 where the split was 87% boys to 13% girls. Ellis for boys has been in the top 100 (barring a couple of years in the early 2000s when it dropped to 103) since 2000 whereas Ellis for a girl has been outside the top 1000 names for nearly ten years now.

I've heard it used for both but I see it as more of a boys' name for some reason.

I only know one Ellis and she’s a woman

Boy.