The reality is you only know your weight when your loaded and ready for the road.
Once loaded I weight the tongue weight. I pressurize the
tires to cold pressure, in my case 50 psi.
My
tires sit on 2x6 boards in our yard. I measure the length of the tire patch area. The length is proportional to the weight on each side. If the lengths and tire pressures are nearly equal, the weight is nearly equal on each side.
I then weight the tongue.
This is my once a year process and tells me everything I need to know about my trailer's weight.
I simply drive my loaded trailer to the transfer station every year before we leave and measure the weight by driving thru the scales.
In some sense it's kind of silly because in the years we've traveled in our Scamp 16, trailer weight and tongue weight have barely moved, 2400 lbs on the
axle and 200 pounds on the tongue.
It's of course possible to do this when you first get your empty trailer.