In kaiju movies and really anything with a huge being, you’ll get the thunderous sound of their footsteps along with maybe things moving and car alarms going off. How large do you have to be for the sound of your steps to be audible from a distance?
Audible to whom, from what distance? You can make the answer anything you want, by tweaking those numbers.
Depends a LOT on the characteristics of the surface one is stepping on.
An elephant can weigh 6 tons. I’ve been at zoos where elephants are walking around making no more sound than cat. An elephant is the largest land animal, so anything you’re seeing in a movie is hyped up for the effect, not a realistic depiction. Think about the energy it takes to create even a low-level seismic tremor. A single animal just couldn’t do that.
A herd of stampeding elephants might create ground vibrations that could be detected from a long distance, but not with a human ear through the air.
I read somewhere that Elephants can “hear” with their feet and communicate with each other by making sounds with their feet.
One of my cats weight 18 pounds. When she comes down the wooden stairs she sounds like a herd of elephants. Yet when she jumps on the bed at night, she’s silent and light as a feather on her feet, until she plops down on my chest.
Whatever my upstairs neighbor weighs. I am always amazed at how much noise some people make when they walk. It makes me want to give them a scholarship to finishing school.
Yet, on the other end of the scale, we have this:
This is a video of some elephants I just filmed on safari in Zambia two weeks ago. You can hear the leaves crunching but to the previous posters’ point, they are utterly silent… creepily so. They actually woke us up with their chewing, but it wasn’t loud, it was just the loudest part about them.
That being said, I am a near 300# dude and my wife and child are less than half my size, but I walk silently in comparison. I attribute it to stronger calf muscles and being more athletic early in life and generally. We had some contractors in our basement once who burst out laughing when they saw me appear because they couldn’t figure out who could have been walking overhead as the footsteps were so light and they knew that my wife and 6 year old daughter had left. So they assumed I was <6 years old and very small and left alone. Then we all had a good chuckle about how loudly they walk.
So, I think as the parrot proved upthread, booming is more about intent than size.
Well, I am small and not particularly heavy. However, I am a tap dancer. I can make a LOT of noise when I walk, even without my tap shoes on. Even barefoot. It’s all about the strike. The ground isn’t gonna shake, but you’ll hear me coming.
I also have two cats. When the two of them get going the ground could shake. Also, they’ve knocked over chairs. As kitttens, they did this. More than once. Even though cats notably do not have a lot of mass.
I can make quite a boom on a kettle drum with just one finger.
A horse makes a sound when running that can be heard from a fair distance, although it would take a fair sized Clydesdale, or Suffolk to get to “booming.” Bison, on the other hand make enough vibration to be felt in your feet. (If you are near a bunch that are running, that is.)
Tris
Where oh, where are the megafauna of days gone by?
How sure are you that sound is not a pair of coconut shell halves being pounded, hollow side down, on a table? 
My sound effects servant knows better. They are to be clapped together under appropriate circumstances.
I’m not at all large, but you can sure hear me coming. I call myself a heel pounder. It’s just the way I walk. My son would always say, “I can always tell when mom comes home. I can hear her walking.” And he would be in his upstairs bedroom! I’ve tried walking differently, but I can’t. Of course, if I concentrate on my walking I can walk softly as to not disturb someone, but otherwise, I pound away.
I always think of one of my favorite Seinfeld moments:
Elaine was complaining about a guy at work that was always hovering and sidling up to her. She says she’s going to give him a taste of his own medicine and sidle up to him.
Jerry: You, sidle? You…you stomp around like a Clydesdale!
When I was an obnoxious teenager, I was able to modify my walk anywhere from “footsteps of a mouse” to “footprints of an elephant” with little visible difference. I would use this ability to annoy people or not as I saw fit.
I would concur. The same five pound bunny who quietly runs about my living room when he’s happy will make an earth shattering ka-boom when he thumps.
In real life large heavy things hitting the ground tend to make an almost subsonic <whump!>. The Hollywood cliche is largely due to the limitations of theater sound systems; you’ll almost never hear realistic gunfire for the same reason.
To me, a reasonable approximation would be when the tree cutters dropped a 20’x7’ poplar log on my lawn while removing the tree. I experienced that as a dinosaur-sized boom and was thankful to be elsewhere.
Hard to estimate a weight… maybe 2 tons or so, dropped from about 20 feet?
Same with cats. Not a sound when walking, but they sound like a herd of buffalo when they’re zooming around the house like they’re possessed.