Impossible to tell from your post as there is too much missing info. Age of house. One story or two story house. Main girder or full width floor joists. Floor Joist size. Pier size. Pier spacing. Loading from above.

Thank you. I can’t answer all those questions. I plan to have a framing carpenter here for other jobs - hopefully he can assess all that if the subfloor is not obviously strong enough.

The house was built in 1989, cape cod style, 1.5 stories, steep roof. The 2nd story loft is over part of the affected areas and supported by other close walls (closets, bathroom). The tub is alongside an exterior wall. I’d have to go into the crawl space to measure the other stuff.

There is an existing tub and laundry. I want to move and stack the washer/dryer, and make sure that the tub will be OK when filled. The fridge I am not too worried about. I think the tile will be OK based on the other info I’ve collected.

I had assumed that the subfloor under the stacked laundry and tub would need to be reinforced. What is the best and easiest way to do that?

UPDATE: Joists are 7.5”. Here are a couple of pics from our temporary crawl space access, showing exterior wall with brick skirt and one of the cinderblock columns which I’m guessing are the piers. The crawl space is messy because the subfloor has rotted and not been replaced yet. All of that (plus the door) is will hopefully be fixed by the framing carpenter. (It is dry now and has been protected with new gutters, tyvek and loose cement boards.)

You can’t see it in these photos, but the adjacent joist is resting on the cinderblock column.

UPDATE 2: If there is a cinderblock column under the tub, do you think that would provide enough support? The tub starts about 8’ away from the cinderblock column in the photo, along the exterior wall. So if I go down into the crawl space, I might find another cinderblock column somewhere under the tub against the back exterior wall.

Don't confuse subfloor with your joists as far as supporting weight. Together, they form a structural support. The most important thing to resist deflection is going to be the joist span and height. You've already said they are 16" on center, which is much better for stiffness than 24" on center. Enter in your numbers here: Deflectolator