A CAT scale weighs your loaded RV and tow vehicle one axle at a time so you can compare the real numbers against the sticker ratings. It costs about $14 to $16 for the first weigh and roughly $4 to $5 for a re-weigh the same day, takes ten minutes, and is the single cheapest way to prove a used RV is actually safe and legal for you to tow before you hand over money. Most overloaded RVs do not look overloaded. They look fine sitting in a driveway, and the problem only shows up when you put each axle on a certified platform.
If you are buying used, weighing is not optional homework. A travel trailer that is 800 pounds over its rated capacity, or a tow vehicle whose rear axle is maxed out before you load a single thing, is a safety problem you inherit the moment you sign. This guide walks you through exactly how to do it, what the ticket means, and what numbers should stop the sale.
Why weighing matters more than the brochure
Every RV has rating plates with numbers like GVWR, GAWR, and (for trailers) GVWR plus a tongue or pin weight. Those are the manufacturer's limits. They are not what your specific used unit weighs today, loaded with a previous owner's leftover gear, a full propane tank, water in the tank, batteries, and a generator.
Dry weight on a brochure is a fantasy number from the factory floor. Real-world "wet and loaded" weight is routinely 1,000 to 2,500 pounds heavier on a mid-size travel trailer or fifth wheel, sometimes more once you add water, propane, batteries, and the stuff people forget to remove. If you tow at or above the limits, you get worse braking, sway, blown tires, voided warranties, and in a crash, liability questions you do not want.
A CAT scale turns all of that guesswork into four hard numbers on a printed ticket. Pair the ticket with the towing math in our RV towability calculator and you will know in five minutes whether this combination is safe for you, not just safe in theory.
The numbers you are checking (plain English)
Before you drive to the scale, learn these terms. They are printed on the RV's federal certification label (usually inside a cabinet, on the frame, or near the door) and on your tow vehicle's door jamb sticker.
| Term | What it means | Where to find it |
|---|---|---|
| GVWR | Gross Vehicle Weight Rating: the most the fully loaded vehicle or trailer is allowed to weigh | Door jamb (tow vehicle) / cert label (RV) |
| GAWR | Gross Axle Weight Rating: the max for one axle (there is a front and rear number) | Same labels, listed per axle |
| GCWR | Gross Combined Weight Rating: the max for truck plus trailer together | Tow vehicle door jamb or owner's manual |
| Tongue weight | Downward force the trailer puts on the hitch (bumper-pull trailers) | Target 10 to 15 percent of loaded trailer weight |
| Pin weight | Same idea for a fifth wheel, on the truck bed | Target 15 to 25 percent of loaded trailer weight |
| Payload | What the tow vehicle can carry: passengers, cargo, hitch, tongue/pin weight | Yellow sticker on tow vehicle door jamb |
The trap that catches most buyers is payload. People assume a "half-ton can tow 10,000 pounds" headline number tells the story. It does not. The truck's payload, often only 1,300 to 1,800 pounds on a loaded half-ton, runs out long before the tow rating does once you add a hitch, a full family, and tongue or pin weight. A fifth wheel loads 15 to 25 percent of its weight straight onto the truck bed, which is exactly where payload gets eaten alive.
How a CAT scale actually works
A CAT scale has three side-by-side platforms in a row, plus sometimes a fourth. You pull forward so each axle group sits on its own platform, and the scale reports the weight on each one separately. That separation is the whole point: it tells you the front axle, the rear axle, and the trailer axles individually, not just one lump total.
You will find CAT scales at truck stops (Pilot, Flying J, TA, Love's, and many independents). Use the free Weigh My Truck app or the catscale.com locator to find one near you. The app even lets you pay from your phone and get the ticket digitally, so you never leave the cab.
The platforms are built for 80,000-pound semis, so your RV will not hurt anything. The attendants weigh trucks all day and will not blink at an RV.
Step by step: weighing the combination
Do this with the RV loaded the way you will actually travel: full propane, batteries in, fuel topped off, and ideally fresh water at your normal travel level (many people travel with the fresh tank low, so weigh how you tow). Bring the person who normally rides with you so passenger weight is real.
1. Weigh fully hitched (the combination pass). Pull onto the scale with the truck and trailer connected and your weight-distribution hitch engaged exactly as you tow.
- Platform 1: truck front axle
- Platform 2: truck rear axle
- Platform 3 (and 4): trailer axle(s)
Push the call button, give the prompt your truck or company info (just say "personal RV"), and wait for the ticket. Note your position number for the re-weigh discount.
2. Re-weigh unhitched (the second pass). Pull off, unhitch the trailer (leave it in the lot if allowed, or do a separate pass), and weigh just the truck. Tell the attendant it is a re-weigh so you get the cheaper rate. This gives you the truck's axle weights with no trailer load.
3. Do the subtraction.
- Tongue or pin weight = (truck rear axle hitched) minus (truck rear axle unhitched), roughly, or more precisely, total combination weight minus trailer-only weight gives you the load transferred to the truck.
- Loaded trailer weight = the trailer axle reading plus the tongue/pin weight it transferred to the truck.
- Truck total = front plus rear axle, compare to truck GVWR.
- Each axle compared to its GAWR.
If the math feels fiddly, that is normal. Write all four ticket numbers down and run them through the RV towability calculator, which does the subtraction and flags overages for you.
Reading the ticket: a worked example
Say you are buying a 32-foot travel trailer and towing with a half-ton truck. Your two tickets read:
- Combination, hitched: front axle 3,400 lb, rear axle 4,200 lb, trailer axles 6,500 lb
- Truck only, unhitched: front 3,500 lb, rear 3,100 lb
Now check it:
- Truck rear GAWR is, say, 3,900 lb. Your hitched rear axle is 4,200 lb. That is 300 pounds over the rear axle limit. Walk-away or fix-the-load territory.
- Tongue weight: rear went from 3,100 unhitched to 4,200 hitched, and the front dropped 100 lb (typical weight-distribution behavior). The trailer is putting roughly 1,200 lb on the hitch.
- Loaded trailer weight: 6,500 (trailer axles) plus about 1,200 (tongue) = roughly 7,700 lb. If the trailer's GVWR is 7,600 lb, the trailer itself is slightly over its own rating.
- Tongue weight percent: 1,200 / 7,700 = about 15.6 percent. That is in the healthy 10 to 15 percent band, just at the top.
In that example, two separate problems show up that no brochure would have told you: the truck's rear axle is over, and the trailer is loaded past its own GVWR. Both are fixable by removing weight, but you now know that before you buy, not after a tire blows on I-80.
What good and bad numbers look like
Use this as a quick gut check. Always verify the exact ratings on the specific unit, since two trailers of the same model can have different axles and tires.
| Check | Healthy | Warning | Walk away (or renegotiate) |
|---|---|---|---|
| Any axle vs GAWR | Under 90% | 90 to 100% | Over 100% |
| Truck total vs GVWR | Under 90% | 90 to 100% | Over GVWR |
| Truck + trailer vs GCWR | Under 90% | 90 to 100% | Over GCWR |
| Tongue weight (bumper pull) | 10 to 15% | 8 to 10% or 15 to 18% | Under 8% or over 18% |
| Pin weight (fifth wheel) | 15 to 20% | 20 to 25% | Over 25% of payload room |
| Trailer vs its own GVWR | 200+ lb headroom | At or near GVWR | Over GVWR loaded |
A trailer that is already at or over its GVWR with the previous owner's leftover gear is a yellow flag worth pricing in. It often means the RV is heavy for its category and you will have very little margin for your own stuff. That is especially common on bunkhouse toy haulers and big Class A motorhomes loaded with water and fuel.
Seller questions and what to ask at the scale
You usually weigh after you are serious but before final payment. Before that, ask the seller:
- "Has this ever been weighed loaded? Do you have a CAT ticket?" A seller who has one and shares it is a good sign.
- "What did you tow it with?" If they towed a 32-foot fifth wheel with a half-ton, the unit may have been chronically overloaded, which stresses axles, tires, and brakes.
- "How old are the tires?" Cross-check with our guide on RV tire age. Overloaded plus old tires is a blowout waiting to happen.
- "Has it ever had axle or suspension work?" Bent axles and worn bushings show up on chronically overloaded rigs.
Conditions to walk away (or drop your offer hard):
- Any single axle reads over its GAWR even lightly loaded.
- The trailer is over its own GVWR with minimal cargo, signaling a heavy build with no margin.
- The seller refuses a quick weigh, or the unit cannot be moved to a scale because of mechanical issues. Inability to move it for weighing can hide bigger problems, the same way it can hide slide-out problems or a soft floor.
Costs and timing, honestly
- First weigh: typically $14 to $16 at most CAT locations (prices vary by state and have crept up, so verify at the specific scale).
- Re-weigh same day, same location: roughly $4 to $5 with the original ticket or app.
- Total time: about 10 to 15 minutes for both passes if the scale is not busy.
- App: Weigh My Truck handles payment and delivers the ticket to your phone, no need to talk to an attendant.
For a $30,000 to $90,000 used RV, spending $20 to confirm it is safe and legal to tow is the best money in the entire buying process. It is cheaper than one new trailer tire and far cheaper than a roadside blowout. Fold the real weight into your total picture with the RV ownership cost calculator, since a unit that needs a bigger tow vehicle changes the math fast.
Putting it all together before you buy
Weighing is one of four "do not skip" used-RV checks, alongside inspecting for water damage signs, confirming the title and lien are clean, and walking the full used RV inspection checklist. A clean weight ticket plus a clean inspection is a strong buy. Numbers over the ratings are not automatically a no, but they are a renegotiation point, a "you need a bigger truck" reality check, or in the worst case, a walk-away.
When you have the listing in front of you and you are not sure whether the truck you own can legally pull it, get your RV verdict and let the numbers tell you before the seller does.
FAQ
Do I need a special scale, or will any truck scale work? A certified CAT scale is ideal because it gives you separate, legal-for-trade readings per axle and a printed ticket. Some farm co-ops, gravel pits, and recycling centers have single-platform scales that only give one total weight, which is far less useful. You want per-axle numbers, so use a CAT scale when you can.
Should the fresh water tank be full when I weigh? Weigh it the way you actually travel. Water is about 8.3 pounds per gallon, so a 40-gallon fresh tank adds roughly 330 pounds. Many people tow with the fresh tank nearly empty and fill at the campground. Weigh both ways if you can, but at minimum weigh your real travel configuration so the numbers reflect how you will use it.
What if the seller will not let me take it to a scale before buying? Ask why. A reasonable seller will allow a short, supervised drive to a nearby CAT scale or meet you at one. If the unit cannot move under its own setup, that itself is a red flag worth investigating. See our RV red flags guide for how to read a seller who blocks basic verification.
My truck can "tow" the trailer's weight on paper. Why weigh at all? Because tow rating is only one of four limits. Payload, rear axle (GAWR), and combined weight (GCWR) all have to pass too, and payload is usually the one that fails first on half-ton trucks pulling a fifth wheel or a heavy Class C motorhome towing a car. A scale is the only way to confirm all four at once.
How often should I re-weigh after I buy? Weigh once loaded the way you travel to set your baseline, then re-weigh any time you significantly change your gear, add a generator, or swap tow vehicles. An annual check is cheap insurance, especially before a long trip.
Paste a listing and get your RV verdict before you ever drive to the scale: /check-rv-listing.