Axle weight, tire count, tire type, and towing speed determine cold inflation pressure. The Trailer Tire Pressure Calculator converts them into a target PSI within sidewall limits.
Calculate Cold Trailer Tire Pressure from Loaded Axle Weight and Tire Count
This calculator converts a trailer’s loaded weight, tire count, and sidewall ratings into a target cold inflation pressure for ST, LT, or P-metric tires. It’s built for RV, utility, boat, livestock, and cargo trailer owners who need to match pressure to an actual load instead of guessing at the number printed on the sidewall.
Entering Your Trailer’s Loaded Weight, Tire Count, and Sidewall Ratings
Enter loaded trailer weight, total tire count, each tire’s max load rating and max cold pressure (from the sidewall), and tow speed, in pounds/PSI or kilograms/Bar. Output is a target cold pressure. The load-to-pressure math is unit-agnostic — it holds as long as weight and pressure stay in one consistent system throughout.
Switching the unit toggle converts existing field values using 1 lb = 0.45359237 kg and 1 psi = 0.0689476 bar, the standard exact and rounded factors used internationally for weight and tire-pressure conversion.
Two mistakes are common on top of the one noted below: entering the sidewall’s warm pressure reading (checked right after driving) instead of its rated cold maximum, and entering axle count instead of total tire count on tandem or triple-axle trailers, which understates how many tires are actually sharing the load.
How the Load-Proportional Cold Pressure Formula Works
Static per-tire load: $$L_{static} = \frac{W}{n}$$ where $W$ is total loaded trailer weight and $n$ is tire count.
This calculator adds a 10% dynamic bias buffer on top of static load, since road crown, cornering, and uneven cargo placement routinely shift more than the theoretical average onto one side of an axle: $$L_{dyn} = L_{static} \times 1.10$$
For P-metric tires, effective load capacity is derated by dividing by 1.10 before any other math runs — a Tire and Rim Association (TRA) requirement for P-metric tires used in trailer and light-truck applications: $$L_{max,eff} = \frac{L_{rated}}{1.10}$$
Target pressure follows the load-to-capacity ratio, scaled against the tire’s sidewall maximum pressure: $$P_{target} = \frac{L_{dyn}}{L_{max,eff}} \times P_{max} \times 1.10$$
This straight-line ratio is a widely used engineering approximation of TRA’s stepped load-inflation tables — it’s a convention documented in tire-fitment technical guides that describe linear interpolation to a table’s reference point, not a fixed physical law, and real TRA tables step in increments rather than scaling perfectly smoothly. The final 1.10 multiplier is this calculator’s own conservative margin on top of that ratio; it is not sourced from a TRA table or any other standard, and exists purely as a built-in buffer.
For highway speeds above 65 mph, TRA’s published ST-tire speed table adds +10 psi (about +0.7 bar) for 66–75 mph, or +10 psi plus a 10% load-capacity reduction for 76–87 mph.
This table applies specifically to ST-designated tires — it has no published equivalent for LT or P-metric trailer tires, so selecting a faster speed tier with those tire types leaves the pressure output unchanged, which is a detail worth knowing before you assume “faster speed” always means “more pressure” here.
The single most common input mistake is entering a tire’s maximum load rating in the “Estimated Loaded Weight” field instead of the trailer’s actual loaded weight — that makes the calculator treat the trailer as running at 100% capacity no matter what’s really on it.
Valid inputs are a loaded weight and tire count both greater than zero, with tire count as a whole number. At very light loads, the straight-line formula above can output pressures in the single digits — a number with no basis in reality, since every pneumatic tire needs a minimum cold pressure well above that just to seat the bead and support its own sidewall structure regardless of load; treat any calculated figure under roughly 20–30 psi as “run the tire’s stated minimum,” not the literal output.
At the other boundary, if the load-based math calls for more pressure than the tire’s stated maximum, the calculator caps the target at that sidewall maximum rather than showing a number above it, because exceeding sidewall maximum risks bead and wheel damage independent of how much weight is on the tire.
Real-world results can still vary with tire age, wheel alignment, road surface, and how evenly cargo is loaded across the axle, so treat the target as a starting point and confirm it with a gauge before every trip.
Where a Load-Based Target Falls Relative to Sidewall Maximum Pressure
Common Questions About Setting Cold Trailer Tire Pressure by Load
Should trailer tire pressure be checked cold or right after driving?
Always cold, before the trailer has moved that day. Driving heats the air inside a tire and raises pressure temporarily; airing down to the target number while warm leaves the tire under-inflated once it cools.
Why is my target pressure higher than a simple load-over-capacity calculation?
This calculator adds two internal buffers on top of the raw ratio: a 10% allowance for uneven side-to-side load and a 10% pressure margin. Neither buffer comes from a TRA table — they’re this tool’s own conservative design choice.
Does the highway speed adjustment apply to LT or P-metric trailer tires?
No. TRA’s published +10 psi (and, above 75 mph, -10% load) speed table is written specifically for ST-designated trailer tires. LT and P-metric tires have no equivalent published speed-inflation table, so a faster speed tier won’t change their result.
What does it mean if the calculator shows my load exceeds tire capacity?
Your trailer’s weight per tire exceeds what these tires are rated to carry, even at maximum pressure. Reduce cargo or move to tires with a higher load rating — increasing pressure past sidewall maximum does not add capacity.
Can I just run ST tires at the sidewall maximum pressure all the time?
Many haulers do, since ST tires are engineered for that pressure. The load-based target gives a lower alternative for lighter loads, which can reduce bounce and uneven wear — but running at sidewall maximum on its own is never unsafe.