About PayloadCheck

What this site is

PayloadCheck is a small set of free calculators for one badly-answered question: whether a particular truck and a particular trailer add up arithmetically against the ratings printed on that truck and that trailer. Not against a brochure figure, not against what somebody with the same badge on the tailgate posted in a forum thread. Four pages do the work:

• Ratings Check — the main tool. You enter the yellow occupants-and-cargo placard number from your driver's door jamb (or, for trucks above 10,000 lb GVWR that may not carry a placard at all, one of two fallbacks: GVWR minus a loaded scale weight, or GVWR minus curb weight clearly flagged as an estimate), what you and your gear weigh, the hitch hardware, the trailer weight on a basis you pick, and the ratings you want tested. It reports each check on its own line: over, no overage found, depends on actual tongue weight, or not entered and therefore not checked. It also lists what it never looked at — axle loads, tire loads, side-to-side balance, brakes, hitch setup.
• Scale Weights — the truck-stop scale method, laid out as three passes with the load held identical between them: truck alone, hitched with weight-distributing bars untensioned, then hitched in travel configuration. It derives raw tongue or pin weight and gross trailer weight from the tickets, and checks loaded axle weights against the GAWR, GVWR and GCWR figures you type in. It exists mostly to kill one specific error, the denominator trap, where dividing tongue weight by the trailer-axle platform reading instead of by true gross trailer weight makes your tongue percentage read falsely high.
• RV Cargo — cargo carrying capacity for a camper, starting from the yellow label on your own unit rather than a calculation, with a GVWR-minus-UVW fallback. It handles the two rules owners most often get backwards: on units labeled under the post-2008 federal rules full propane is already inside the unloaded vehicle weight, while fresh water is cargo at roughly eight and a third pounds a gallon.
• Why Payload First — a reference page rather than a calculator: a glossary of GVWR, GAWR, GCWR, placard payload, tongue and pin weight, curb weight versus UVW, and CCC, each term quoted from its defining source and paired with where you physically find that number on your vehicle.

All of it runs in your browser. Nothing you type is transmitted, there is no account, and there is no app. Most of these pages get opened standing in a dealer lot or a driveway, on a phone, next to the trailer somebody is about to buy.

Who builds it

PayloadCheck is built and maintained by one person — an independent developer. I am not an engineer, not a certified weight inspector, not a mechanic, not an RV technician, and not a dealer. This site is not affiliated with, sponsored by, or endorsed by any vehicle, trailer, or hitch manufacturer, nor by SAE International, NHTSA, or CAT Scale. Nobody pays to appear here, no calculator steers you toward a product, and no page is sponsored. The site is funded by advertising, which is disclosed in the privacy policy. This page carries no advertising at all.

Be blunt about what that means for how you read the site: there is no professional judgment here about your rig. None. The value is that every constant, definition and published range is traceable to a source you can open and check yourself, that the arithmetic between them is tested, and that the tool refuses to guess when it does not have enough information.

Where the numbers come from

This is safety-adjacent subject matter, so the standard is stricter than elsewhere: two independent authorities for every towing figure, with quotes kept on file, and a fixed hierarchy when they disagree — the labels on your vehicle outrank the owner's manual, which outranks the manufacturer's towing guide, which outranks the regulation, which outranks component labels, which outrank everything secondary.

• Definitions — 49 CFR 571.3 for GVWR, GAWR, GCWR and curb weight, quoted verbatim on the glossary page and cross-checked against how the Ford and GM towing guides word the same terms.
• The placard — FMVSS No. 110 (49 CFR 571.110), including its required statement and, importantly, its scope: the standard applies to vehicles of 4,536 kilograms (10,000 pounds) or less. Heavier trucks sit under a different labeling regime and may carry no such placard, which is why the tool offers fallbacks instead of pretending every truck has one.
• Tongue weight draws on payload — the controlling statements come from the manufacturers' own guides, Ford's 2026 and GM's 2025, both of which state that adding tongue load together with passengers and cargo must not push the vehicle past its rear axle rating or its GVWR. Corroborated in the RV context by the motor-home label language at 571.110 S9.3.4(e), where a towed trailer's tongue weight counts as cargo.
• Tongue and pin percentage ranges — the authorities genuinely differ, so the band is preserved rather than averaged into a false single number. Conventional trailers: GM publishes 10 to 15 percent, CURT about 10 to 15, Weigh Safe 9 to 15. Fifth-wheel and gooseneck: GM and Ram publish 15 to 25 percent independently of each other — Ram’s body builder guide words it as more than 15 and less than 25 percent of maximum trailer weight — with RVSEF giving the same band and etrailer calling roughly 20 percent typical. Ford is the dissent: its current guides assume a flat 15 percent, so a Ford owner reading a factory figure is reading the bottom of everyone else’s range rather than the middle. Ford and Ram separately rate trailers at a flat 10 percent conventional tongue load when computing ratings, which is a test assumption, not an operating recommendation, and the site says so.
• Rating assumptions — attributed to each manufacturer's own guide, never generalized across the industry, alongside SAE J2807 as the uniform test standard for combined and trailer weight ratings.
• The scale method — CURT and Weigh Safe, with the fifth-wheel variant per etrailer. CAT Scale's own how-to is used only for platform positioning and is not credited with the method. The caution that a platform ticket cannot see a side-to-side overload comes from the Escapees SmartWeigh program.
• RV labels and cargo capacity — 49 CFR 571.110 S9 plus RVSEF. Where a manufacturer's own blog contradicts the federal labeling rule on propane, the page does not adjudicate it; it tells you to trust the label on your unit.
• Constants — water at 8.34 lb per gallon from USGS (the label rounds to 8.3), propane at 4.24 lb per gallon from AmeriGas with Ferrellgas at 4.2, and cylinder tare weights from published cylinder specifications.
• Sway — triple-sourced: NHTSA's towing publication DOT HS 809 433, plus Weigh Safe and CURT, all three warning that too little tongue weight invites sway.

A number with no source next to it is a defect. One previously-shown figure — a weight range for fifth-wheel hitch hardware — was deleted outright during an audit because no authority could be produced for it; the tool now sends you to that hitch's spec sheet instead. That is the intended behavior when sourcing fails.

How the math is checked

Every calculator's logic is re-implemented independently in a test harness and checked against fixed expectations rather than against whatever the page happens to output. The suite currently runs 143 assertions with zero failures, and nothing ships unless it is green.

The tests worth naming are the ones that guard against a wrong answer in the dangerous direction. A property test over 500 random cases proves displayed rounding always runs against the user: margins round down, overages round up, consumption rounds up. The combined-weight check is tested for double counting, so occupants already sitting in a scale weight are never added a second time and tongue weight is never added separately into combination math. A blank occupants field can never produce a passing result. A tongue weight you measured at one load cannot certify a hypothetical maximum-load scenario. And the denominator trap is pinned by a worked example, including the wrong answer, so a regression would be caught immediately.

The suite also tests the words. It enforces the no-permission-language rule described below, and it enforces that boilerplate pages such as the privacy policy carry no advertising code. This does not make the site infallible — a test can only check the formula it was given — but a typo in a constant or a silently broken check gets caught before you read it.

What this site will never tell you

It will never tell you that a combination is safe, legal, within spec, or fine to tow. There are no green lights here, and that is deliberate.

The tools compare numbers you typed against ratings you typed. They cannot see your tires or their inflation, your brakes, your hitch installation, how the load sits side to side, the condition of your suspension, the crosswind on the pass, or what your state's rules require of you. The results are worded to make that limit unmissable: verdicts read OVER A RATING, INCOMPLETE, RESULT DEPENDS ON ACTUAL TONGUE/PIN WEIGHT, or NO OVERAGE FOUND IN THE CHECKS COMPLETED — never a word that grants permission. Blank inputs become "not checked," never "assumed fine." The banner on the main tool says it plainly: PLANNING CHECK ONLY — NOT PERMISSION TO TOW.

The authorities are your vehicle's certification label and yellow placard, your trailer's data plate, the labels on the hitch components themselves, your owner's manual and the manufacturer's ratings, and the law wherever you are driving. This site is a planning aid that shows its arithmetic. Where the two disagree, the site is wrong. As the scale page puts it: estimates plan, scales measure.

The assumption that moves the answer most

The Ratings Check asks for sixteen numbers, two dropdown choices and three either-or selections. Nearly all of the numbers are things you can go outside and read: a placard, a data plate, a scale ticket, a rating stamped into a hitch shank. Two of the choices are not readings at all. They are assumptions — what share of the trailer’s loaded weight will sit on the hitch, and which style of hitch you are using. Those two assumptions move the final answer further than anything you can measure, which is exactly backwards from how most people approach the problem.

Here is the arithmetic, worked with round illustrative figures rather than any particular truck. Say the yellow placard reads 1,700 pounds, four hundred pounds of people get in, and a hundred pounds of equipment is already bolted on. Five hundred pounds of the placard is spent before the trailer is touched, leaving 1,200 pounds for the tongue. Divide that leftover by the tongue percentage and you get the figure the tool labels the payload-limited trailer weight — a mathematical planning limit, not a towing rating:

Nothing was measured differently between those four rows. The truck is the same truck, the people are the same people, the gear is the same gear. Within the conventional band the answer moves by 4,000 pounds, a factor of exactly 1.50×. Within the fifth-wheel band it moves by 3,200 pounds, a factor of exactly 1.67×. Across both bands, from the most generous corner to the least, the spread is exactly 2.50× — because 25 divided by 10 is 2.5, and the leftover payload cancels out of the ratio entirely. That last point is worth sitting with: the ratio does not depend on your placard, your passengers or your gear. Change every input and the spread stays 2.5×. It is a property of the published ranges, not of your truck.

This is the whole reason the tool refuses to collapse a band into a single number. Averaging the conventional band to 12.5 percent would print one confident-looking figure of 9,600 pounds and quietly bury a spread of four thousand. Most people’s real margin is a few hundred pounds. An averaged assumption can be wrong by ten times the margin it is being used to evaluate. So the tool shows both ends, and when the low end clears a rating while the high end does not, it stops and says RESULT DEPENDS ON ACTUAL TONGUE/PIN WEIGHT rather than picking a side. The authorities themselves do not agree here — GM and CURT publish roughly 10 to 15 percent for conventional trailers and Weigh Safe publishes 9 to 15, while GM and Ram independently publish 15 to 25 percent for a fifth-wheel pin and Ford’s current guides dissent with a flat 15. Averaging across that disagreement would be inventing a number no authority stands behind.

The denominator trap, with the arithmetic

The Scale Weights page exists mostly to kill one error, and the error deserves to be shown rather than described. Three passes over a truck-stop scale with the load held identical between them. Truck alone: 7,000 pounds total. Hitched, reading the truck’s axles only: 8,000 pounds. Hitched, reading the whole combination: 15,000 pounds.

Tongue weight is the first difference: 8,000 minus 7,000, or 1,000 pounds. Gross trailer weight is the second: 15,000 minus 7,000, or 8,000 pounds. One thousand over eight thousand is 12.5 percent, comfortably inside the conventional band.

Now the trap. The ticket also shows the trailer’s own axles at 7,000 pounds — 15,000 minus the 8,000 under the truck. It is right there on the paper, it is labelled as the trailer, and dividing by it feels obvious. One thousand over seven thousand is 14.29 percent. Same trailer, same ticket, same afternoon, and the figure has moved nearly a point and a half. The reason is structural: the trailer’s axles carry gross trailer weight minus whatever the tongue is holding, so using that reading as the denominator subtracts the numerator out of the denominator. The relationship is fixed — the wrong figure equals the true one divided by one minus the true one — which means it is not a random error. It always overstates, and it overstates more the heavier the tongue already is:

The 12.5 percent row alone burns through 36 percent of the conventional band’s entire five-point width. The row to remember, though, is the fifth-wheel one: a pin sitting at a true 20 percent — the middle of the published 15-to-25 band, and the share etrailer describes as typical — reports as exactly 25.00 percent by the wrong denominator, which is the top of the range. Not approximately: the identity 20 divided by 0.80 lands on 25 exactly. A reader doing that division would conclude they were at the ceiling of every published recommendation while actually sitting in the middle of it.

Direction is what makes this worth a page. The error never tells you that you have too little tongue weight; it always tells you that you have more than you do. And the published warnings all point the same way — NHTSA’s towing publication, Weigh Safe and CURT independently caution that too little tongue weight invites sway. A reader who believes they are pinned against the upper limit is being handed a reason to shift load rearward, off the tongue, on the strength of a percentage that was never real. So the tool never asks for that denominator at all. It derives gross trailer weight from the passes themselves, and it rejects the ticket outright when the combination total does not exceed the truck-alone weight by substantially more than the tongue weight, because that pattern means the passes got mixed up before any percentage was computed.

Three tools, one subtraction

Read the source of the three calculators side by side and they collapse into a single line: a margin is a limit you did not choose, minus every load you did. Ratings Check subtracts occupants, equipment and tongue weight from the placard. Scale Weights subtracts each axle or total reading from the matching GAWR, GVWR or GCWR. RV Cargo subtracts fresh water, gear, anything installed after the label was printed, and any propane beyond what the label already counted, from the cargo capacity on the label. Everything else on those pages is bookkeeping about where the limit legitimately comes from and what honestly counts as a load.

Saying it that plainly makes one connection visible that people routinely miss, because it crosses between two of the pages. A load you add to the camper does not stay in the camper. Fresh water is cargo on the RV side at 8.34 pounds a gallon; on the truck side that same water arrives at the hitch at the tongue percentage. Run it through both bands and every gallon of fresh water costs between 0.83 and 1.25 pounds of truck payload — 0.834 at a 10 percent tongue, 1.251 at 15.

Which produces a rule of thumb that is, by accident of the constants, almost exactly right: at a 12 percent tongue, one gallon of fresh water is one pound off your truck’s placard. Eight point three four times 0.12 is 1.0008. So a 40-gallon fill is 334 pounds of camper cargo and roughly 42 pounds of truck payload at a mid-band 12.5 percent — the same forty-two pounds counted twice, in two different budgets, and it has to clear both. Nobody who fills the tank at the campground gate is thinking about the driver’s door jamb, but the placard is where the water lands.

The two published constants for water are worth a sentence too, because the site chose between them. USGS gives 8.34 pounds a gallon; the federal RV label rounds to 8.3. Across a full 100-gallon tank the entire disagreement is four pounds — less than half a gallon of water. The tool uses the larger figure, not because the smaller one is wrong, but because consumption should round against the reader rather than for them. When two sources differ by less than the sloshing in the tank, the tie goes to the stricter one.

Rounding that is always against you

Every displayed figure on this site is rounded deliberately in one direction, and the size of that bias is bounded and worth stating. There are three layers. Consumption figures round up to the whole pound. Margins then step down to the next ten pounds; overages step up to the next ten. A margin the arithmetic puts at 206 pounds is displayed as 200; an overage of 168 pounds is displayed as 170.

Worst case, that whole stack understates a margin by less than eleven pounds — under two from the round-up-and-round-down pair, under ten from the ten-pound step — no matter how large the numbers are. The bound matters as much as the direction. An unbounded conservative bias is just noise: if the rounding could shave hundreds of pounds off a margin, readers would learn to distrust it and mentally add the difference back, which defeats the purpose. Eleven pounds is less than a full jerry can of water, it never moves the other way, and a property test over five hundred randomly generated cases proves the direction cannot invert.

None of which makes an answer correct. Rounding conservatively on top of an assumption you could not verify does not verify the assumption — it just stops the display from flattering it. The tongue percentage in the first section of this page can be wrong by four thousand pounds of trailer; no amount of careful rounding touches that. Which is the same conclusion the scale page reaches by a different road: estimates plan, scales measure.

How often it's reviewed

Pages that quote a regulation, a manufacturer guide, or a published range are re-checked against those sources at least twice a year, and immediately when a source changes — a new model-year towing guide, a revised federal standard, a superseded publication. Pages carrying a "Reviewed" stamp have actually been re-checked on that date; the stamp is a promise, not decoration. The current review pass is July 2026.

Corrections

If a figure here is wrong, a source has been superseded, or a page is worded in a way that could lead somebody toward a bad towing decision, say so: [email protected]. Corrections outrank new features, and wording that edges toward permission language is treated as the most urgent category of all. Include the page and, if you have it, the publication that contradicts what is written — that turns a fix from a research project into ten minutes.

Privacy, briefly

Your weights, your ratings and your scale tickets stay on your device. The calculators are plain JavaScript running in your browser; there is no server that receives your figures, because no server is involved beyond delivering the page. Nothing you enter is placed in a web address or an analytics event. Full details, including how the advertising on the calculator pages works, are in the privacy policy.