hello,
have 28ft 3 axle enclosed trailer, would like to get it weighed with car in it, local landfill/transfer station has scale, do I need to unhook it or can I just drive truck off scale, or weight truck/trailer then just truck?

IMO most scales are somewhat busy , I pickup material for my boss and am scaled quite a lot , I drive on empty then with the load so they get a weight to charge for the ... opposite when I drop a load of scrap at the junk yard. I doubt they will let you disconnect the trailer on the scale as it will take to much time thus tying the scale up for to long . They should if there is room allow you to disconnect the trailer and weigh the truck separately then just subtract the truck weight from the total of the truck and trailer combination for your loaded trailer weight.

Seems to me that the most accurate weight would be found disconnected.
Tongue weight is supported by hitch & truck; that could be calculated by weighing separately, but would only be approximate, I think.
Reason I say that is that it seems that trailer weight forward of the axles contributes to tongue weight.

I would say disconnected. If you are using weight distribution bars I am sure they would also throw the weight off.

thanks, scale is just a couple of miles from home, will just weight truck/trailer then go back and weight truck

Our local scrap yards have drive on scales with digital readouts, Just drive on, jot down your weight, drop your trailer where convenient and safe, drive back on, do the subtraction, no cost, no hassle. no wait. But our vehicle scales are only accurate to 20lbs?

The only diiference being hooked to the truck will be tounge weight. Make sure it doesnt have distribution bars connected when weighing. Tounge weight for that trailer should be around 600lbs. So scale weight plus 600 should be very close.
Doug

If you can see an outside display board drive the truck on with the front axle only first and write that down, then both axles and then with the front axle of the trailer on, if those scales are long enough, and finally with both trailer axles on the scale only.
If no visible out side display ask the operator before driving it on to see if they will do that for you
BTW, every car trailer sales folks I have ask about the unladen (empty) weight lied about their brands being way lighter than they actually were by a bunch, 2980 lbs. unladen advertised versus 4350 actual
Oregon has a bunch of commercial truck scale stops all over the state hat they don't keep open 24/7, they are mainly single axles or dual axles at the most. Very short scales but they all have outside displays so you can use them any time you want when they are closed by driving on them slowly
Our local garbage dumps do have long scales.
They charge by the ton to dump garbage at the dumps, you have to use them before and after dumping your loads there

Use the CAT scales app and go to a truck stop. Weigh the whole thing then just the truck. Don't even have to go inside.

For work my truck has increased GVWR stickers for the trailer, which is weighed attached to the truck. I have to weigh front axle then truck rear, then trailer axles and add it all together to get the GVWR for the trucks registered weight. You can move weight around on the trailer though to change what shows up on the trailer axles and what will show up on the truck's axle in case one is too heavy.