You need three numbers from your vehicle: max payload, GVWR, and max tow rating. Payload and GVWR are on your door placard. Max tow is in your owner's manual or the manufacturer's online tow guide. Curb weight is optional but improves accuracy — leave it blank to estimate from GVWR minus payload. GCWR auto-estimates from GVWR + max tow if you don't enter it, but the real value from your owner's manual is always better.
Enter the trailer curb weight (empty weight) and trailer GVWR (max loaded weight). Both are on the trailer's VIN plate or tongue sticker. You can enter a trailer without a vehicle, or a vehicle without a trailer — the calculator adapts.
Use the sliders for trailer cargo, vehicle cargo, and passengers. Adjust tongue weight if you know the actual number (default is an estimate at 10% of loaded trailer weight). The calculator updates in real time as you move the sliders.
Five progress bars show how much of each limit you're using. Green means fine, amber means you're getting close (80%+), and red means you've exceeded a limit (100%+). The status bar below the bars gives you a plain-language verdict, and the explainer tells you which constraint is the bottleneck and what you can do about it.
Select your state or province in the towing rules section. The calculator tells you whether your trailer weight requires brakes and shows the relevant statute.
Tip: Save frequently-used setups as profiles (up to 10). Use the Share button to send a link — the recipient gets your specs pre-filled and can save them locally.
tomaTow can save up to 10 named setups (profiles) in your browser and generate shareable links. Everything stays local — no account required.
Your current inputs are automatically saved to your browser as you type. If you close the tab and come back, everything will be right where you left it. This happens silently in the background — you don't need to do anything.
Fill in at least one vehicle or trailer value. The Save button won't activate on a completely empty form.
You'll be prompted to name the profile (up to 40 characters). Give it a descriptive name — something like "F-150 + 16ft flatbed" or "Mom's Equinox + popup."
Once saved, the profile selector appears in the header. Switch between saved setups at any time using the dropdown.
Note: Profiles store your vehicle and trailer specs (ratings), not per-trip values like cargo, passengers, or tongue weight. Loading a profile zeros those fields so you can enter each trip's actual load.
Load a profile from the dropdown, make your changes, then click Save setup again. You'll be offered two choices: Update [name] (overwrites the existing profile) or Save as new (creates a second profile). To rename or delete profiles, use the Manage profiles panel — it appears below the header whenever at least one profile is saved.
Your current specs are encoded into a URL and copied to your clipboard automatically.
Paste it anywhere — text, email, forum post. The link contains everything: vehicle specs, trailer specs, and your selected state or province.
Their browser decodes the URL locally and pre-fills the calculator with your specs. A "Save this setup?" banner appears so they can add it to their own saved profiles. Their existing profiles are untouched.
Privacy note: Shared links encode specs directly in the URL — no data passes through our servers. Anyone with the link can read the encoded specs, so don't share links that include information you'd rather keep private.
Open the driver's door and look at the vertical frame the door closes against — that's the door jamb. You'll find a white or yellow sticker somewhere on it, often near the latch. It may also be on the door edge itself (the narrow strip facing you when the door is open).
A line labeled GVWR followed by a weight — e.g. 7000 LB or 3200 kg. Enter this in the GVWR field.
A line reading something like "The combined weight of occupants and cargo should not exceed X." That number is your payload limit. Enter it in the Max payload field.
The sticker also shows GAWR Front and GAWR Rear (per-axle ratings). You don't need those for this calculator.
Trailer curb weight and GVWR can be found in several places. Check these in order:
Look for a metal plate riveted to the trailer tongue or A-frame, near the coupler. It lists the trailer's GVWR (sometimes labeled "Gross Vehicle Weight Rating" or just "Max Weight") and may include curb weight. This is the most authoritative source.
Many trailers also have a paper or adhesive label on the tongue or driver-side frame rail. It often lists GVWR, curb weight (sometimes called "empty weight" or "shipping weight"), and axle ratings.
Check your bill of sale, the manufacturer's website (search by model number), or the original spec sheet. Useful if the VIN plate is weathered or missing.
Weigh the trailer empty at a certified scale (CAT scale, ~$12). That gives you curb weight directly. For GVWR, contact the trailer manufacturer with your VIN — they can look it up.
tomaTow checks five constraints simultaneously. Every towing setup must satisfy all five — the weakest link is your true limit. Each constraint has a progress bar:
Each bar turns amber at 80% and red at 100%. The 80% warning is a heads-up, not a hard limit — it means you're getting close and should pay attention. At 100%, you've exceeded a manufacturer rating.
By default, tongue weight is estimated as a percentage of the loaded trailer weight (curb + cargo). The default is 10%, which is the low end of the typical 10–15% range for a properly loaded trailer. You can adjust the percentage or enter a known tongue weight if you've measured it.
If you don't enter a GCWR, the calculator estimates it as GVWR + max tow. This is often optimistic — the real GCWR accounts for engine, transmission, and cooling limits that the simple sum doesn't. The real number from your owner's manual is always better.
The most common towing mistake isn't hooking up too heavy a trailer — it's ignoring payload. People look at their vehicle's tow rating, compare it to the trailer's weight, and stop there. If the truck can tow 8,000 lb and the trailer weighs 6,000 lb, it must be fine. But tow rating is only one of the five constraints, and it's rarely the one that runs out first.
Payload is the hidden bottleneck. Your vehicle's payload limit covers everything riding on the vehicle itself: passengers, cargo in the bed or cabin, and tongue weight from the trailer. That last one catches people off guard. The tongue pushes down on the hitch with roughly 10–15% of the loaded trailer weight — on a 6,000 lb trailer, that's 600–900 lb of payload consumed before you've put anything else in the truck. Add a driver, a passenger, and some gear in the bed, and a half-ton pickup with a 1,400 lb payload rating can be over the limit while the tow rating bar is still green.
This is especially common on mid-size trucks and crossover SUVs. Their tow ratings have climbed impressively — 7,000 lb, even 8,000 lb — but payload hasn't kept pace. A vehicle might be rated to pull a trailer it can't safely carry the tongue weight of once you account for people and gear.
That's exactly what tomaTow is designed to show you. Instead of checking one number against one rating, the calculator runs all five constraints at once. The weakest link — usually payload — is your real limit, and it's the number most people never check.
State and provincial trailer brake thresholds cover all 50 US states, Washington DC, and 10 Canadian provinces. Each entry includes the weight threshold, a citation to the governing statute, and a direct link to the statute text (where a stable URL exists).
Data was cross-referenced against multiple sources to catch errors:
| Source | Used for |
|---|---|
| NATM 2021 | National Association of Trailer Manufacturers brake law survey. Primary reference for US state thresholds and citations. |
| RVIA 2017 | Recreation Vehicle Industry Association compliance guide. Secondary US reference for threshold cross-checking. |
| Camping World 2025 | Published state-by-state brake requirement summary. Used as a third cross-reference for US data. |
| RVDA.ca | Recreation Vehicle Dealers Association of Canada. Primary reference for Canadian provincial thresholds. |
| CanLII | Canadian Legal Information Institute. Used to verify Canadian provincial statute text directly. |
| State/provincial statutes | Direct statute text consulted for every jurisdiction. Links provided inline in the calculator where stable URLs exist. |
Five US states (Kansas, Kentucky, Missouri, Oregon, and Wyoming) have performance-based braking statutes rather than a specific trailer weight threshold. For these states, the calculator shows 3,000 lb as a conservative default and notes that the statutory requirement is performance-based.
Five Canadian provinces (British Columbia, Manitoba, Nova Scotia, Prince Edward Island, and Saskatchewan) don't have stable deep-links to the relevant statute sections. The calculator shows the citation text without a clickable URL. The threshold data is verified against RVDA.ca and CanLII.
The five constraints (trailer load, tow rating, tongue weight, payload, and GCWR) use straightforward arithmetic from the manufacturer ratings you enter. No proprietary formulas — the calculator compares your loaded weights against the published limits. The tongue weight estimate (default 10% of loaded trailer weight) follows industry guidance for a properly loaded conventional trailer.
This calculator is not a substitute for certified scales or professional advice. It gives estimates based on the numbers you enter. Certified scales (CAT scales at truck stops, ~$12) give actual axle weights — the only reliable way to know your real tongue weight and total trailer weight.
Auto insurance risk: Exceeding manufacturer ratings can void your coverage in an accident. An overloaded vehicle can give your insurer grounds to deny the claim.
Aftermarket modifications: Lifts, airbag suspension, and sway bars affect real-world capability but don't change your manufacturer ratings — those are sticker specs for stock vehicles.
CDL threshold: In the US, a commercial driver's license (CDL) may be required at 26,001 lb (11,794 kg) GCWR. The calculator flags when you approach or exceed that number.
Towing laws change. The brake thresholds and statute links in this calculator are reference values. Always verify current requirements with your state DMV or provincial licensing authority before towing.
tomaTow runs entirely in your browser. Your vehicle specs, trailer specs, and saved profiles are stored in your browser's localStorage — nothing is sent to a server. There are no accounts, no tracking, no analytics, and no cookies. If you clear your browser data, your saved profiles go with it.
When you use the Share button, your specs are encoded into the URL itself (as a base64 parameter). The recipient's browser decodes it locally — no data passes through our servers.
The site is hosted on Netlify as a static file. There is no backend, no database, and no server-side code.