There's a few ways to measure tongue weight.

Our first recommendation would be to take your vehicle and trailer to a nearby commercial scale. Commercial scales can be found at truck stops, landfills, quarries, and supply centers. Here's some helpful websites that will locate commercial scales near you https://www.publicscaleslocator.com/, https://catscale.com/cat-scale-locator/.  There is typically a small fee when utilizing a commercial scale. In order to calculate your tongue weight you need to do the following:

1. Make sure your trailer is fully loaded as it would be when taking it on a trip. Drive all 4 wheels of your vehicle on the scale while your trailer is still attached. Record the weight. DO NOT drive your trailer on the scale with your vehicle. You are getting the weight of your vehicle only while under load.
2. While the vehicle is still on the scale, unhook the trailer and lift the tongue jack high enough so that there is no weight on the hitch ball. Again, be sure that no part of the trailer is on the scale. Record the weight. This is the weight of your tow vehicle.
3. Subtract the two weights from each other to give you your tongue weight.

While you are at the scale we always recommend getting the weight of your boat and trailer package too. This is helpful for verifying if you have the correct tow vehicle and trailer capacity.

Our second recommendation would be to use the bathroom scale method. Although it's at the convenience of being at your own home it does require some supplies and set up. You will need a bathroom scale, 2 pieces of steel pipe, a concrete paver or brick (or something that is the same thickness as your scale so that your set up is level), 2'x4' between  four to five feet long and possibly some extra pieces of wood to use to get your coupler the same height as your vehicle's tow ball would be. The idea is to set the tongue of  the trailer onto a beam that spreads the load between the bathroom scale and another support point. The load represented on the bathroom scale is the ratio of the scale (A) to the coupler support distance (B) and the tongue support distance (C). If there is a 3' gap between the scale support pipe to the coupler support and a 1' gap between the opposing support pipe to the coupler, that equates to a 4:1 ratio. You'll want to set your 2'x4' up using a 3:1 or 4:1 ratio. In the example below we are using a 4:1 ratio, which we recommend for heavier trailers.

1. Chock your trailer tires.
2. Lay the brick/paver or similar item and the bathroom scale three feet apart.
3. Lay one pipe long ways on the scale and one long ways on the brick/paver.
4. Set your 2'x4' on top of the pipes.
5. Mark the 2'x4' one foot over from where it rests on the pipe that is on the brick/paver. This is where you will rest the tongue of the trailer on additional block(s) of wood.
6. Measure 3 feet over from your first mark, and center the other piece of pipe long ways under the 2'x4'.
7. Place the tongue of your trailer on of the first mark you made in step #5. Here's where you may need to use some extra pieces of wood to get your coupler at the same height as your vehicle's tow ball.
8. Get the reading on bathroom scale and multiply it by 4 since the weight on the scale is at the 4:1 ratio.

*diagram reference: www.boatus.com

Our third recommendation would be to purchase a tongue weight scale. There's a variety of models available. Here are two popular manufacturers.

https://www.haulgauge.com/

https://www.sherline.com/product/sherline-trailer-tongue-weight-scale/