How it works
The beam works as a lever. One end rests on a block (a pipe on a brick works well) and the other on a pipe on the bathroom scale. The tongue jack stands on the beam between them. The closer the jack is to the block, the smaller the share of the load the scale carries, so you can measure a tongue several times heavier than the scale’s limit.
Tongue weight = (scale reading − beam reading) × distance between supports ÷ distance from jack to block
Setting it up
- Place a block and the scale on level ground, with a short pipe on each so the beam can rock freely.
- Lay a sturdy beam (a 4×4 or steel tube) across the two pipes and note the scale reading.
- Lower the tongue jack onto the beam at the chosen distance from the block, with the coupler at towing height.
- Read the scale and enter the distances, measured from the center of each pipe to the center of the jack foot.
Worked example
Supports 36 in apart, jack 12 in from the block, beam alone reads 10 lb, with the trailer it reads 210 lb. Trailer weighs 5,000 lb.
- Multiplier: 36 ÷ 12 = 3
- Tongue weight: (210 − 10) × 3 = 600 lb
- Share: 600 ÷ 5,000 = 12%, inside the 10–15% range.
Common setups
| Supports apart | Jack to block | Jack to scale | Multiplier |
|---|---|---|---|
| 24 in | 12 in | 12 in | Halfway: reading × 2 |
| 36 in | 12 in | 24 in | One third: reading × 3 |
| 48 in | 12 in | 36 in | One quarter: reading × 4 |
| 36 in | 24 in | 12 in | Two thirds: reading × 1.5 |
Pick the setup that keeps the scale reading under its capacity with some room to spare. A larger multiplier lets you weigh more, but small measuring errors are multiplied too, so measure distances carefully.
Once you know the tongue weight, compare it with the recommended range in thetongue weight calculator, and if it is off, use thetrailer load balance calculator to see where to move the cargo.
Common mistakes
- Measuring to the scale instead of the block. The jack distance is measured from the support that is not on the scale.
- Forgetting the beam. Its weight on the scale is not tongue weight; subtract it.
- Weighing an empty trailer. Measure with the trailer loaded as you will tow it, water tanks included.
- Using a soft surface. Grass or gravel lets the supports sink and the beam tilt. Use concrete.