"Tranny" and "shemale" are the slurs most commonly used against trans people online, according to a study.
Anti-bullying charity Ditch The Label and its analytics partner Brandwatch described the harassment as being "inhumane".
Researchers analysed 10 million posts on the topic of transgender identity, shared from the UK and the US over a period of three-and-a-half years.
They said more than 1.5 million of them were anti-trans.
Other common transphobic themes of online posts included misgendering people - purposefully labelling somebody as a gender that they do not identify as.
Video streaming sites and message boards were found to host the most transphobic abuse and the "least constructive conversation" about trans lives.
"This report uncovers the shocking and inhumane ways in which transgender people are targeted, harassed, and abused on digital platforms," said Ditch the Label's chief Liam Hackett.
"Using the largest dataset of its kind, it is easy to see how, left unchallenged, digital hate speech can and does evolve into acts of physical violence committed towards trans people."
'Hurt and hopeless'
Kenny Ethan Jones is a transgender male model and activist.
"Transphobia is something I witness every single day," he told the BBC.
"I'm often intentionally misgendered and I'm always on the receiving end of comments like, 'You're not a real man,' 'You're confused and you need God,' 'You don't deserve to live.'
"I wonder if people understand the effect that these abusive comments have on my mental health.
"Some days I feel hurt and hopeless."
The study compared transphobia across a range of sites, including social media, blogs, news outlets and forums.
Larger sites such as Twitter and Instagram had the lowest percentage of abuse in general discussion around trans issues, at 5% and 12% respectively.
Whereas on video streaming site YouTube, 78% of such discussion was abuse. Researchers said it should be noted that the volume of posts on this site was much lower than Twitter and Instagram.
Comments sections on news sites made up much of its abuse total (19%), and forums featured a high percentage of abusive language (40%).
Meanwhile, mentions of trans issues across most of the site categories were more hostile in the US.
The BBC has approached Twitter, Instagram and YouTube for comment.
Politics and race
The transphobic insult "tranny" featured more than 1.2 million times between 2015 and 2019, accounting for 80% of the insults studied.
"Shemale" had 150,000 mentions.
The researchers also found examples of dead-naming: purposefully using a transgender person's previous name from before they transitioned.
In the UK, politics appeared to be a key theme associated with the abuse, with the topic appearing in 27% of all the transphobic posts.
Race came a close second. It was raised in 24% of the transphobic messages, and was especially common when the abused person was black.
In the US, race was found to be the main driver, appearing in 34% of the abusive comments, followed by politics, which was raised in 33%.
Parenting topics were also seen to be used as triggers for transphobia, with people using their parental status - "as a mother of two kids…" - to justify their views. This type of abuse tended to centre around the parents' fears, for example not wanting their children to be around trans people.
In addition, transphobic slurs were used by some sports fans alongside racist, sexist and homophobic abuse, even when the intended victim did not identify as transgender. For example, Serena Williams had transphobic insults directed at her because she was not deemed to look feminine enough.
'Why is transphobia a free-for-all?'
Jay Hulme is a 22-year-old children's poet from Leicester. He's a transgender man and he says he constantly receives harassment on social media because of his identity.
"It can be a full-scale hate storm with thousands of people attacking me relentlessly for days, or individual accounts sending general hate. I've been called an abuser, a sexual harasser, a sexist. I think the worst ones would have to be the times people call me a paedophile, just because I'm trans and write books for children.
"About four or five months ago I started an instant block policy when it comes to anyone who sends me harassment on Twitter. As of today, I've blocked almost 5,000 accounts who reached out and sent me transphobic messages."
He thinks social media companies should do more to prevent their platforms being used for hate speech.
"Online harassment of trans people is a really prevalent problem, and often goes a lot further than the things people say in real life.
"Social media companies should do more, but I think there's a lack of understanding of transphobia within their teams so they struggle to counter it. Also, they should do more for all kinds of hate - their moderation tactics have been proven ineffective time and again."
For more stories like this, follow the BBC LGBT correspondent Ben Hunte on Twitter and Instagram.