Trailer Tire Load Calculator

How This Tire Load Calculator Works

Every trailer tire has a stamped load rating, and quietly exceeding it is one of the most common causes of a blowout. This tire load calculator flips the question people usually get backwards. Instead of adding up tire capacities, it starts from your trailer's total weight and tells you how much each tire is actually carrying, then what rating you should be running. Enter your GVWR and axle count and you'll know, in seconds, whether your tires are truly up to the job.

How to Use This Calculator

Two inputs give you your per-tire load and the rating you need.

1. Enter your trailer GVWR. Put in the trailer's gross vehicle weight rating, the most it should weigh fully loaded. The default is 7,000 lbs, and you can edit it.
2. Select your number of axles. Choose 1 axle (2 tires), 2 axles (4 tires), or 3 axles (6 tires). The tool converts axles to tires automatically.
3. Read your load per tire. The calculator divides the GVWR across your tires to show how much weight each one carries.
4. Read your recommended tire rating. It adds a 10% safety margin and rounds up to give the minimum tire load rating you should buy. Check that number against the rating on your tire sidewalls.

How It's Calculated

The logic is deliberately the reverse of the usual assumption. Rather than "add up what my tires can hold," it asks "given everything the trailer can weigh, how much lands on each tire, and what rating covers that safely?"

Tires = axles x 2

Load per tire = GVWR / number of tires

Recommended rating = round up (load per tire x 1.1) to the next 50 lbs

That 1.1 is a 10% safety margin, and rounding up to the next 50 lbs matches how tires are actually rated and sold. Here's how axle count becomes tire count:

Notice that adding an axle spreads the same weight across more tires, which lowers the load on each one. That's a big reason heavier trailers ride on two or three axles rather than one.

Why start from GVWR instead of your typical load? Because GVWR is the worst case the trailer is built to carry, and tires need to survive that worst case, not just an average day. If you sized your tires to a light load and then filled the trailer to its limit, the tires would be the thing that gives. Working from the top down, GVWR to per-tire load to rating, means your tires have margin no matter how you pack, which is exactly the safety-first way to think about it.

Worked Example: A 7,000 lb Trailer on 4 Tires

Say you have a 7,000 lb GVWR trailer with 2 axles, which means 4 tires.

Find the load per tire. 7,000 divided by 4 tires is 1,750 lbs on each tire when the trailer is loaded to its GVWR.

Add the safety margin and round up. 1,750 x 1.1 is 1,925 lbs, and rounding up to the next 50 lbs gives a recommended rating of 1,950 lbs per tire. So you'd want tires rated to at least 1,950 lbs each.

Now picture the same 7,000 lb trailer on 3 axles instead. The weight spreads across 6 tires rather than 4, so the load per tire drops to about 1,167 lbs, and the recommended rating drops accordingly. That's the whole point of the tool: your tire needs follow directly from your weight and how many tires carry it. Since GVWR drives this, it pairs naturally with the Payload Calculator and the Axle Capacity Calculator, and heavier trailers also call for a stronger hitch, which the Hitch Class Calculator covers.

Tips and What to Watch

Read the rating off your sidewall, don't guess. Every trailer tire has its maximum load stamped on the sidewall. Compare that number to the recommended rating rather than assuming the tires that came on the trailer are enough.

The 10% margin is there for a reason. Real loads shift, roads are hot, and no one loads perfectly evenly. The safety margin gives your tires headroom so a normal bad day doesn't put them over their limit.

Match all your tires to the same rating. Your weakest tire sets your real limit, so a single under-rated tire undoes the others. Keep every tire at or above the recommended rating.

Under-rated tires fail under load and heat. A tire run over its rating builds heat and is far more likely to blow out, especially at highway speed on a hot day. If your tires come in under the recommendation, replace them before you load heavy.

Keep them inflated to the rating. A tire only delivers its stamped load rating at its rated pressure, so an underinflated tire is effectively under-rated even if the sidewall number looks fine. Check cold pressures before every heavy tow, since a soft tire runs hot and carries less than it should.

Frequently Asked Questions

What does the number on the tire sidewall mean?

Trailer tires are stamped with a maximum load rating, the most weight that tire is designed to carry at its rated pressure. That's the figure you compare against the calculator's recommended rating. If the sidewall number is lower than the recommendation, the tire is under-rated for your trailer.

Why add a 10% margin?

Because real-world loads are never perfectly even and conditions vary. A 10% cushion covers uneven loading, heat, and the occasional heavier-than-planned trip, so your tires aren't running right at their limit. It's cheap insurance against a blowout.

Do all the tires on my trailer need the same rating?

Yes. Your trailer is only as safe as its weakest tire, so every tire should meet or exceed the recommended rating. Mixing in one under-rated tire creates a weak point regardless of how strong the others are.

What happens if I use under-rated tires?

They build excess heat under load, wear unevenly, and are much more prone to sudden failure, especially at speed. A blowout on a loaded trailer can cause loss of control, so running properly rated tires is a genuine safety issue, not just a spec detail.