How to Weigh Your RV at a CAT Scale and Actually Understand the Ticket

You are sitting at a Flying J at half past six in the morning, engine running, staring at a painted rectangle in the tarmac divided into three sections with no instructions anywhere. There is a speaker box on a post to your left. Behind you sits a Peterbilt whose driver has done this four thousand times and is not going to explain it.

That is the moment most people quietly decide to skip it and go get coffee.

Learning how to weigh your RV at a CAT Scale is probably the highest-value hour you will ever spend on your rig, and it is over in eight minutes once you know the sequence. The number will not be pretty. It rarely is. But it replaces the fiction printed in the brochure with what your axles are actually carrying today, with your gear aboard, your water aboard and your kids in the back seat.

The part nobody explains well is that one pass over the scale does not answer the question you came with. It gives you four numbers. Getting tongue weight, or pin weight, or the effect your weight distribution hitch is having on the front axle, takes two or three passes and some subtraction. That is the bit this post spells out.

The short answer

Pull onto the CAT Scale so each axle group sits fully inside its own platform section: truck front axle on platform 1, truck rear axle on platform 2, trailer axles on platform 3. Set the parking brake, stay in the vehicle, press the intercom button, and give a company name (your surname works) and a truck number (1 works). Collect the ticket at the fuel desk or take it in the Weigh My Truck app.

The ticket prints STEER, DRIVE, TRAILER and GROSS. That is your front axle, your rear axle, your trailer’s own axles, and the whole combination. To get tongue weight you need a second pass with the trailer dropped: tongue weight equals the truck’s axle total hitched minus its axle total unhitched. Weigh loaded the way you actually travel, not empty, and compare every number to your own door sticker rather than any brochure.

What a CAT Scale actually measures, and what it does not

A CAT Scale is a certified public truck scale, the kind you find at Pilot, Flying J, Love’s, TA and a long list of independent truck stops. The platform is split into sections, usually three, sometimes four on longer scales built for split-weight loads. Each section weighs whatever is sitting on it. That is the entire mechanism.

Which means the scale measures axle groups, not vehicles and not wheels. It cannot tell you what your left rear tyre is carrying. It cannot separate your tongue weight from your truck’s rear axle weight, because as far as the scale is concerned those loads arrive through the same pair of tyres and are indistinguishable. Everything clever you do with a CAT Scale comes from weighing the same rig in two different configurations and subtracting.

Readings come in 20 lb increments, so do not chase the last ten pounds. If two passes disagree by 20 or 40 lb, that is rounding and normal fuel sloshing, not a discovery.

CAT Scale also publishes a guarantee that they will stand behind a ticket if you are cited for being overweight after weighing legal on their scale. That guarantee is written for commercial drivers, not RVers, but it tells you something useful anyway: these scales get maintained and inspected because someone’s livelihood depends on them.

What it costs and how the reweigh discount works

Prices vary by location and they have climbed steadily. Budget somewhere around 15 US dollars for a first weigh in 2026 and check the actual number on the sign or in the app before you commit, because I would rather you find the current price yourself than trust a figure in a blog post that ages badly.

The reweigh is the part that makes multi-pass weighing affordable. Go back over the same scale, within 24 hours, and you pay a small fraction of the first price. The conditions matter and people get burned by both of them:

• It must be the same physical scale, not another location of the same chain.
• You must give the same company name and truck number, spelled the same way. If you said “Okafor” the first time and “Okafor RV” the second, the system will not match them and you will pay full price again.

So a three-pass session costs one full weigh plus two reweighs. Not much money for numbers you will use for years.

The Weigh My Truck app is worth installing before you go. You pay in the app, the scale recognises you, and the ticket arrives on your phone as a PDF. No intercom conversation, and you have a permanent record instead of a thermal-paper receipt that fades to blank in a glovebox by September.

Getting loaded the right way before you go

Here I would take a different line from the usual guidance on the standard advice. Most guides tell you to fill everything: fresh water full, fuel full, propane full, so you capture the worst case. That is a useful data point and I am not against it. But it is not the number you should be planning around, because most people do not tow with 60 gallons of fresh water sloshing behind them.

Weigh how you actually travel. If you run a quarter tank of fresh and fill at the campsite, weigh with a quarter tank. If you are a boondocker who leaves the driveway with everything topped off because the next water is 200 miles away, weigh that way instead. The point of the exercise is to find out what your rig weighs on the road, not to generate a hypothetical.

Practical checklist for a meaningful weigh:

• Fuel: full, or note the level. Diesel runs roughly 7.1 lb per US gallon, so half a 34-gallon tank is about 120 lb of difference. Enough to matter.
• Fresh, grey and black tanks: at your normal travel levels. Water is 8.34 lb per US gallon and it is the single biggest variable in the whole rig.
• Propane: full bottles. They are rarely empty when you leave.
• People and pets: aboard, in their normal seats. Yes, including the dog.
• Everything you actually carry: tools, generator, e-bikes, the awning mat, the levelling blocks, all of it.

If you want a sense of how fast that last line adds up before you drive anywhere, the companion piece on what everything in your RV actually weighs totals a family’s real load item by item.

Pulling onto the scale: the actual procedure

1. Approach from the truck lane, not the car lane. Scales sit off to the side of the fuel islands. Follow the signs for the scale, and if there is a queue, join it and wait. Do not cut in from the fuel island.
2. Line up straight and go slowly. You want the whole rig square on the platform, not angled across it. Two or three miles per hour.
3. Place your axles inside the section lines. Front axle on section 1, rear axle on section 2, trailer axles on section 3. There are usually painted lines or metal seams marking the boundaries. Any axle straddling a seam gives you a garbage reading.
4. Stop, put it in park, set the parking brake. Take your foot off the brake pedal. Some drivers also recommend against leaning on the door, which sounds like superstition but costs you nothing.
5. Stay in the vehicle. Getting out changes the weight by your body mass, and on some scales it triggers an error.
6. Press the intercom button and speak. “First weigh, company name Okafor, truck number 1.” If it is a reweigh, say “reweigh” and give exactly the same name and number.
7. Wait for the green light or the “you’re done” call. Then pull forward, clear the platform completely, and park.
8. Collect the ticket at the fuel desk, or open it in the app. Check the date and time on it, because you will want that for the 24-hour reweigh window.

If you are travelling alone and the intercom feels awkward, the app removes that step entirely. I use it for the record-keeping as much as the convenience.

Reading the ticket line by line

The ticket gives you STEER, DRIVE, TRAILER and GROSS. Those labels were written for a tractor-trailer and they map onto RVs a little differently depending on what you are driving.

The single most misread line is TRAILER. It is not what your trailer weighs. It is what your trailer’s axles are carrying, which excludes everything resting on the hitch. A 9,600 lb travel trailer with 1,250 lb on the tongue prints about 8,350 lb on the TRAILER line. People see that, compare it to a 10,400 lb trailer GVWR, and conclude they have 2,000 lb of room. They have 800.

A note on tag-axle Class A coaches: if your drive axle and tag axle will not both fit inside one platform section, a standard three-section scale cannot give you a clean split. Some longer CAT Scales have a fourth section that solves this. Otherwise you are looking at a scale with individual platforms or an RV rally weigh service.

A worked three-pass session, with the arithmetic

Say Dale and Renata run a crew-cab three-quarter-ton diesel and a 32-foot bunkhouse travel trailer with a weight distribution hitch. They want four things: their real trailer weight, their tongue weight, their tongue weight percentage, and proof the hitch is doing its job. Here is a session with example figures. Your numbers will be nothing like these, which is the whole point.

Pass 1: hitched, WDH bars engaged, loaded for a trip.

• STEER 4,480
• DRIVE 4,860
• TRAILER 8,520
• GROSS 17,860

Pass 2: same rig, back on the scale with the WDH bars released (coupler still on the ball, chains off the brackets).

• STEER 4,300
• DRIVE 5,210
• TRAILER 8,350
• GROSS 17,860

Pass 3: trailer dropped in the back lot, truck alone, both of them and the dog still aboard.

• STEER 4,460
• DRIVE 3,800
• GROSS 8,260

Now the subtraction.

Trailer’s real gross weight = GROSS hitched minus truck alone = 17,860 − 8,260 = 9,600 lb. That is what the trailer weighs, loaded, right now. Not the 7,900 lb dry weight on the brochure.

Tongue weight = trailer gross minus what the trailer axles carry with the bars off = 9,600 − 8,350 = 1,250 lb.

Cross-check it the other way. Truck axles hitched, bars off = 4,300 + 5,210 = 9,510. Truck axles unhitched = 4,460 + 3,800 = 8,260. Difference = 1,250 lb. Two methods, same answer, which is how you know you did not fumble a pass.

Tongue weight percentage = 1,250 ÷ 9,600 = 13.0%. Comfortably inside the 10 to 15% band for a bumper-pull, and if that band is new to you, the full explanation of tongue weight and sway covers where those numbers come from. To run the division across a few loading scenarios, a percentage calculator saves you squinting at a phone keypad on the scale apron.

What the hitch is doing: the truck’s front axle sat at 4,460 lb unhitched. Coupling the trailer dropped it to 4,300, a loss of 160 lb, because the tongue load levers weight off the front. Engaging the bars brought it back to 4,480, which is 20 lb above where it started and inside the scale’s own rounding. That is a properly set up hitch. The bars also pushed 170 lb back onto the trailer axles (8,350 to 8,520), which is exactly why you check trailer axle limits with the bars engaged, not released.

Now compare to the stickers. Suppose the truck’s door jamb says GVWR 10,000 lb, front GAWR 5,200, rear GAWR 6,340, and payload 2,470 lb.

• Truck gross hitched, bars on = 4,480 + 4,860 = 9,340. Under 10,000 by 660 lb.
• Front axle 4,480 against 5,200. Fine.
• Rear axle 4,860 against 6,340. Fine.
• Payload used = 9,340 − (10,000 − 2,470) = 9,340 − 7,530 = 1,810 lb of the 2,470 available. 660 lb spare, which agrees with the GVWR check, as it must.
• Trailer axles 8,520 against a combined trailer GAWR of 10,400 (two 5,200 lb axles). Fine.
• Trailer gross 9,600 against a trailer GVWR of 10,400. 800 lb of cargo capacity left, not the 1,880 the TRAILER line seemed to suggest.

Dale and Renata are legal on every ceiling. They are also 660 lb from the truck’s GVWR, which is thinner than it sounds once you add a second cooler and a passenger’s mother for a week.

Rather than doing this arithmetic on a napkin at the fuel desk, put the four ticket numbers into the RV Payload Calculator and it separates trailer gross, tongue weight, percentage and remaining payload for you, then shows you which ceiling you are closest to. It runs entirely in your browser, so your weights never leave your phone, which matters more than it sounds like it should when the numbers are unflattering.

The passes you need, depending on what you drive

You do not always need three passes. Match the session to the question.

• Travel trailer, want tongue weight and hitch verification: three passes, as above.
• Travel trailer, only want to know if you are legal: one pass, hitched, bars engaged. Compare STEER and DRIVE to the GAWRs, STEER plus DRIVE to the truck’s GVWR, TRAILER to the trailer’s axle rating, GROSS to GCWR. You will not learn tongue weight.
• Fifth wheel: two passes. Hitched, then truck alone. Pin weight is the truck’s axle total hitched minus unhitched, same subtraction. There is no WDH to release, so you skip the middle pass.
• Motorhome, no toad: one pass. Front axle on section 1, rear on section 2, both against their GAWRs and the sum against GVWR.
• Motorhome with a toad: one pass gets coach front, coach rear and toad axles. A second pass with the coach alone gets the toad’s own weight by subtraction.

For a Class A or a Class C, the number you are hunting is cargo carrying capacity: GVWR minus the coach as it sat when it left the factory, minus fluids, minus people. The CCC Weight Calculator handles that split, and the GVWR Calculator is the one for checking axle-by-axle against ratings.

Where a truck stop scale falls short: four-corner weighing

A CAT Scale averages left and right. It has to; the platform is one load cell assembly per section. So an axle reading 4,860 lb might be 2,300 on the left and 2,560 on the right, and the scale will never tell you.

This matters more in RVs than in cars, because RV mass is not distributed symmetrically. The refrigerator, water heater, kitchen slide, awning and often the fresh tank tend to cluster on one side. Add a generator in a curbside bay and a full water tank and you can build a meaningful lean without noticing.

Two consequences. First, a tyre can be over its rated capacity while the axle looks fine, and a tyre that is quietly running 200 lb over its rating on a 95°F afternoon in Nevada is how blowout stories start. Second, side-to-side imbalance changes how the rig behaves in a crosswind and in an emergency lane change.

Individual wheel-position weighing is the fix, and you get it at RV rallies from services like the RV Safety & Education Foundation and the Escapees SmartWeigh programme. They roll portable pads under each wheel, one position at a time, and hand you a sheet with four or six numbers on it plus a tyre pressure recommendation matched to the heaviest wheel on each axle. It costs more than a CAT Scale weigh and you cannot do it on a Tuesday whenever you feel like it. Once every few years is plenty for most people.

Get a CAT Scale ticket this month, because it is available and cheap. Book a four-corner weigh when one turns up at a rally you were going to anyway. Do not let the perfect one stop you doing the available one.

What goes wrong

Straddling a seam. The most common ruined pass. An axle sitting half on section 2 and half on section 3 produces numbers that add up to a correct gross with nonsense in the middle. If your steer plus drive plus trailer does not equal your gross, something is off the platform entirely. If it does equal gross but a line looks wildly wrong, you probably straddled.

Weighing empty. A weigh taken on the way home from the dealer, before the rig is loaded, feels great and tells you nothing. Cargo, water and people are usually 1,000 to 2,000 lb in a family trailer.

Comparing to dry weight. Brochure dry weight excludes options, dealer-installed equipment, batteries, propane, and sometimes appliances. The number on the yellow sticker on your trailer, showing cargo carrying capacity for that specific unit, is the one that counts, and even that assumes empty tanks.

Burning fuel between passes. If you fuel up between pass 1 and pass 3, your subtraction is wrong by the weight of the fuel. Forty gallons of diesel is about 284 lb. Weigh first, fuel second.

Losing the 24-hour window. You get home, look at the ticket, realise you need the truck-alone pass, and drive back the next afternoon. Too late, and it is a different scale anyway because you stopped at a different exit. Plan all your passes as one session.

Assuming ratings are transferable. Two trucks with the same badge, the same year and the same engine can differ by several hundred pounds of payload depending on cab, drivetrain, sunroof, and every option box that got ticked. Ratings are per-vehicle. Your door jamb sticker is the authority, not a forum post about the same model.

A word on rules and limits

Weight enforcement for recreational vehicles varies by state and by country, and it changes. Some jurisdictions require RVs over a certain gross weight to stop at weigh stations; most do not. Some require a non-commercial special licence above a certain combination weight, and California, Texas, Michigan and several others each handle it differently. If you are crossing borders or running near any threshold, check the current rules published by the state or provincial authority that applies to you rather than relying on general guidance, including this page.

The manufacturer ratings on your stickers are a different matter. They are not a legal speed limit you can shade by 5%. They are the engineering basis for the brakes, tyres, bearings, springs and frame on your specific vehicle, and being over them is a bad fact to be holding in any conversation that follows an incident.

Frequently asked questions

How much does it cost to weigh an RV at a CAT Scale?

Budget somewhere in the region of 15 US dollars for a first weigh, with a much cheaper reweigh if you go back over the same scale within 24 hours. The price has drifted upward over the years and varies by location, so check the price on the scale sign or in the Weigh My Truck app before you commit. A full three-pass session is one full weigh plus two reweighs.

Do I need to unhitch my trailer to get tongue weight?

Yes, if you want tongue weight from a CAT Scale. You weigh the truck and trailer together, then drop the trailer somewhere safe off the scale and weigh the truck on its own. Tongue weight is the difference between the truck’s axle weights hitched and unhitched. One pass alone cannot give you that number, because the scale cannot separate tongue load from truck weight on the same tyres.

Should I weigh my RV with full fresh water tanks?

Weigh it the way you actually travel. If you normally roll with a quarter tank and fill at the campground, weigh it that way, because that is the load your axles carry on the road. A second weigh with tanks full is a useful worst-case check, but do not treat it as your baseline unless you genuinely tow full. Water at 8.34 lb per gallon swings the answer hard.

Which CAT Scale platform does each axle go on?

The scale has three sections in a line. Front truck axle on the first, rear truck axle on the second, trailer axles on the third. For a motorhome towing a car, the coach front axle goes on the first, the coach drive axle on the second, and the towed car on the third. Keep each axle fully inside one section, because an axle straddling a seam ruins the reading.

What do I say on the intercom if I do not have a company name?

Give your surname as the company name and 1 as the truck number. Nobody minds. RVers do this every day and the scale operator only needs something to print on the ticket and to match your reweigh against. Use exactly the same wording if you come back for a second pass, or the system will not match them and the discount will not apply.

Can a CAT Scale tell me if my RV is loaded heavier on one side?

No. A CAT Scale weighs a whole axle at a time, so it averages left and right together. Side-to-side differences of a few hundred pounds are common in RVs because appliances, tanks and slide rooms cluster on one side. Individual wheel-position weighing at an RV rally, using portable pads under each wheel, is the only practical way to see it.

How this plays out in practice

Pick a truck stop with a CAT Scale on a route you already drive, load the rig the way you actually travel, and plan three passes in one visit rather than one pass you will have to repeat. Bring a pen. Write the numbers on the ticket as you go, because thermal paper fades and phone photos get lost.

Then do the subtraction the same day, while you still remember which pass was which. Trailer gross, tongue weight, percentage, payload remaining. Drop them into the payload calculator if you want the ceilings checked for you. Four numbers that tell you whether the next trip is a holiday or a slow-motion problem, and if you are over on one of them, the fix is usually a few hundred pounds of things you have not opened since 2023.