Weighing It — Why the Usual Scales Do Not Fit, and What Does

Introduction

Everything in the previous volumes depends on two measurements: tongue weight and trailer gross weight. Both turn out to be awkward to get, for a reason that is easy to miss.

The finding: this rig is too light for the equipment sold to weigh it. Tongue-weight scales are built for travel trailers and fifth wheels with tongue loads of 500 to 1,500 lb. Portable wheel scales are built for commercial trucks. At a 74 lb tongue and a 570 lb wheel load, this trailer falls below the useful range of both, and using them anyway produces numbers with more error in them than the quantity being measured. ⚠ UPDATED 2026-09-16: this volume was written for a 155 lb tongue. The tongue is now 101.5 lb, heading for a 119–126 lb window, which makes the finding stronger, not weaker — every instrument criticised below is being asked to work well down its range.

The good news is that the right answer is cheaper than the wrong one, and the second half of this volume proposes something better than weighing at all for routine use.

4.1 Why the standard tongue scale does not work here

The common recommendation is a Sherline hydraulic tongue weight scale. The smallest is the LM-1000, a 0–1,000 lb hydraulic gauge, and it is a well-made instrument.

It is also the wrong instrument for a 74 lb tongue, for two independent reasons:

Its graduations are 20 lb apart. Reading 74 lb means interpolating between marks on an analogue gauge — and the entire acceptable window for this trailer is 30 lb wide, which is barely more than one graduation.

Its accuracy is specified against full scale, not against the reading. The gauge is warranted to ±2 percent at mid-range, falling to ±3 percent at the extremes. On a 1,000 lb instrument that is ±20 to ±30 lb:

Table 1 — Its accuracy is specified against full scale, not against the reading.** The gauge is warranted to ±2 percent at mid-range, falling to ±3 percent at the extremes. On a 1,000 lb instrument that is **±20 to ±30 lb

Actual tongue weight	What an LM-1000 might read
74 lb	anywhere from 44 to 104 lb

🔴 That span is wider than the entire quantity being measured. The instrument cannot distinguish “correct” from “sway risk” from “over payload.” Sherline makes nothing smaller than the LM-1000, so there is no version of this product that fits.

⚠ This is a general trap worth naming: an instrument’s accuracy is usually a percentage of its full scale, not of what it is reading. A big scale used at the bottom of its range is not a precise small scale. It is the same reasoning that makes a bathroom scale useless for weighing coffee.

4.2 What does work: a platform scale

A digital platform or shipping scale with a 660 lb capacity and 0.1 lb resolution costs about $30 to $45. At 74 lb the reading sits at roughly 11 percent of range — low, but a digital load cell’s error is specified against full scale as an absolute figure, and at 0.1 lb resolution that is still two orders of magnitude finer than anything the load plan needs to distinguish. ⚠ A 300 lb scale would be the better buy at today’s tongue weight if the trailer’s own axle loads did not also need reading.

⭐ The cheap tool is the accurate one here, purely because it is correctly sized.

The method:

Park on level ground and chock the trailer’s wheels. 🔴 Do this first and do not skip it — the trailer is about to sit on a jack with its brakes doing nothing.
Build the scale up to ball height. The coupler must sit at the same height it does when hitched, or the load shifts across the axle and the reading is wrong. Stack solid blocking under the scale until the top of the support column puts the coupler at towing height.
Put a spreader between the coupler and the scale platform — a short steel plate or a block of hardwood. A coupler is a point load and a shipping scale platform is thin sheet; without a spreader it will dish.
Lower the tongue onto the column with the trailer’s jack, then wind the jack fully clear, so all of the tongue load is on the scale and none is on the jack.
Read it. Then wind the jack back down before removing anything.

⚠ All the usual conditions apply: trailer level, loaded exactly as it will be towed, and measured twice — once with the water full and once with it empty — because the consumables shift the balance as they are used.

4.3 Why the certified-scale trick works for axles but not the tongue

A common suggestion is to weigh the truck alone at a certified scale, then again with the trailer coupled, and take the difference as tongue weight. For this rig that does not work, and it is worth understanding why so it is not attempted.

Certified truck scales read in 20 lb graduations. The truck alone weighs somewhere near 5,400 lb, and with the trailer connected its axles carry roughly 74 lb more. Taking a small difference between two large, coarsely-quantised numbers compounds the error of both — a realistic uncertainty of ±20 to ±40 lb on a quantity that is itself only 74 lb. ⭐ It is still worth doing as a cross-check, because the same visit gives the axle weights the load plan needs anyway, and because a 45 lb correction is exactly the size of change this rig is looking for — well inside what the method can see.

🔴 The difference method has more error than the entire tolerance. It is not a matter of being careful.

⭐ The same scale is excellent for everything else, though, and the trip should still be made:

The truck’s front and rear axle weights — the scale ticket the whole load plan has been waiting on. At 2,500–3,000 lb per axle, a 20 lb graduation is under 1 percent.
The trailer’s axle weight, reported directly when the whole rig is weighed. At about 1,150 lb, 20 lb is 1.7 percent — perfectly adequate.

⭐ And that gives trailer gross weight without weighing the trailer separately:

Trailer gross = trailer axle weight (from the certified scale) + tongue weight (from the platform scale)

One trip to a certified scale plus one $40 platform scale produces every number in this project. That is the whole measurement problem solved, for well under $100.

4.4 The wheel-scale option, and why it is not recommended

For completeness: the “proper” way to weigh a trailer portably is a pair of wheel load scale pads, one under each tyre, with the tongue supported at towing height on a third scale. Trailer gross is then simply left wheel + right wheel + tongue.

⚠ The equipment does not suit this trailer. Portable commercial wheel scales such as the Intercomp PT300 start at 10,000 lb per pad — a 580 lb wheel load would sit at under 6 percent of range — and a two-platform system runs to several thousand dollars. Racing scale sets are better matched but still cost four figures.

A pair of 1,000 lb platform scales would work and would cost a fraction of that. It is a reasonable purchase for someone who wants a physical number every time. But there is a better answer for routine use, and it is the next section.

4.5 The better answer for every trip: calibrate once, compute thereafter

The stated problem is that the loadout changes every trip — weather, terrain, how many people are coming. Weighing the rig every time is impractical, and it is also unnecessary.

⭐ Weighing is how you calibrate. Arithmetic is how you plan. Every item’s weight is already known. What changes between trips is which items are aboard and where they sit — and both of those are inputs to a calculation, not to a scale.

A loadout calculator now lives with this dive at 02-inputs/worksheets/Overlanding-Loadout-Calculator.xlsx, generated by build_loadout.py. Set the quantity for each item, set the position of the water on the rail, and it returns:

Trailer gross weight, and how much of the 2,000 lb trailer capacity is used
Tongue weight in pounds and as a percentage
The truck’s total load and its payload margin
A pass or fail against both limits — the 10 percent sway floor and the payload ceiling

The tongue calculation is the Δtongue = W × d / L relationship from vol 2, applied per item: each entry carries a position in inches forward of the axle, and weight over the axle contributes nothing.

⚠ It is only as good as its constants, and three of them are currently estimates that the calibration trip replaces:

Table 2 — ⚠ It is only as good as its constants, and three of them are currently estimates that the calibration trip replaces

Constant	Current value	How to get the real one
L, coupler to axle	126 in (estimated)	Tape measure, trailer level
Trailer tare tongue weight	50 lb (estimated)	Platform scale, empty trailer — a one-time constant
Trailer tare weight	400 lb	Manufacturer, probably fine

⭐ The bare-trailer tongue weight is the one people forget, and it matters because it is the part of the tongue load that no amount of cargo repositioning changes. Measure it once, on the empty trailer, and it never needs measuring again.

Then re-weigh only when something structural changes — a new rack, a different tent, a modification to the trailer. Routine trip-to-trip variation is what the calculator is for.

4.6 What the calculator says about the default loadout

⚠ UPDATED 2026-09-16. This block described a loadout that no longer exists — a hardshell tent, eight gallons of water on the rail and the fridge aboard. On the current always-a-trailer baseline, with the bin gear on the trailer’s front deck, the calculator returns:

Table 3 — ⚠ UPDATED 2026-09-16. This block described a loadout that no longer exists — a hardshell tent, eight gallons of water on the rail and the fridge aboard. On the current always-a-trailer baseline, with the bin gear on the trailer's front deck, the calculator returns


Trailer gross	1,194.1 lb — 40% of capacity
Tongue weight	101.5 lb — 8.50% 🔴 below the 10% floor
Truck total	1,075.5 lb
Payload margin	✅ +24.5 lb

🔴 Note that the two verdicts now disagree, and that is the point of running both. The payload check passes with 24.5 lb in hand; the tongue check FAILS by 17.9 lb. ⚠ The payload margin is not spare capacity — closing the tongue means moving about 38 lb onto the front of the trailer, which spends most of it on purpose.

⭐ That is exactly why a calculator is worth more here than on a truck with 400 lb to spare: the two limits pull in opposite directions, and a configuration can pass one while failing the other. 🔴 Never close the tongue gap by trimming tongue weight to protect the payload number — that buys a legal figure with a control problem.

🔴 And two lines in the calculator have no weight at all — the camp chairs and the grill are carried as FILL, unweighed and counted as zero, so every figure above is a lower bound.

It also demonstrates the trim control working. The water sits 30 inches forward of the axle in that configuration — the front end of the rail — and it is doing real work. Move it to the aft end and tongue weight drops by about 32 lb, taking the trailer below the sway floor. The rail is not decoration.

4.7 What to remember

Buy a 660 lb platform scale, not a tongue scale. The tongue scale sold for this job has more error in it than your entire tolerance.

Make one trip to a certified scale, loaded as you would tow. It gives the truck’s axle weights and the trailer’s axle weight, and with the platform-scale tongue reading it gives trailer gross.

Measure the empty trailer’s tongue weight once, and measure L once. Those two constants make the calculator trustworthy.

After that, compute rather than weigh — and re-weigh only when the rig itself changes.

References

Sherline Products — LM-1000 hydraulic trailer tongue weight scale: 0–1,000 lb, 20 lb gauge graduations, accuracy warranted to 2% at mid-range and 3% at the extremes of the gauge range.
Digital platform and shipping scales, 660 lb capacity with 0.1 lb readability, widely available at roughly $30–45.
Intercomp — PT300 portable wheel load scale: individual capacities from 10,000 lb; multi-platform systems priced in the thousands.
Certified truck scale practice — 20 lb graduations, and the resulting unsuitability of small-difference measurements.
Trailer Build vols 1–3, this project — the trailer as built, the rail as a trim control, and the tongue-weight target.
02-inputs/worksheets/build_loadout.py, this dive — the calculator and its constants.