Tire Pressure Calculator

How to use this calculator

1. Enter your total loaded weight. That's the vehicle plus everyone and everything in it right now — curb weight + passengers + cargo. Not sure? Use your GVWR (on the door placard) for the worst-case fully-loaded number, or hit a truck-stop CAT scale for the real figure.
2. Pick your weight split. Front-wheel-drive cars carry ~60% on the front; SUVs sit near 55/45; a loaded pickup shifts rearward. The preset sets how the load divides across the axles.
3. Set your tire's load index and load range. The load index is the number right after the size (235/65R17 108H → 108). The load range is SL or XL on a passenger tire, or the C/D/E/F letter on an LT tire — it fixes the reference pressure the rating is measured at.
4. Add trailer tongue weight if you're towing. Roughly 10–15% of the trailer's loaded weight presses straight down on your hitch and rides the rear axle. The rear PSI climbs to match.
5. Read the per-axle cold PSI. That's the minimum pressure to carry the load safely. Save the link (your inputs stay in the URL) or export a one-page PDF for the glovebox.

Why this is different from a "recommended PSI" lookup

Most tire-pressure pages — including our own Recommended Tire Pressure Lookup — answer one question: what does my door sticker say? That's the right tool when your vehicle is stock and lightly loaded. But the placard is a single number set for the factory tire at a nominal load. It doesn't help when:

• You're towing or hauling heavy. A 700-lb tongue or a bed full of gravel loads the rear axle far past the placard assumption. The rear tires need more air, and the placard won't tell you how much.
• You've changed tires. Plus-sized, upsized for off-road, or swapped from P-metric to LT — the new tire has a different load index and reference pressure, so the old sticker number no longer maps to the same load capacity.
• You want the real engineering number. This calculator uses the same load-and-inflation relationship the tire industry publishes — capacity scales with pressure — instead of a one-size placard.

No automotive result on page one of "tire pressure calculator" computes per-axle load or handles tongue weight and dually rears. Most of the top results are bicycle calculators. This one is built for trucks, trailers, and anyone running non-OE tires — and it's embeddable, ASE-authored, and shows its formula.

How the math works

A tire's load capacity isn't fixed — it rises and falls with inflation pressure. Every tire's load index (its rated load) is defined at a specific reference pressure set by the tire's type. So to find the pressure needed for a lighter load, you scale down from that reference:

required cold PSI = reference PSI × (load per tire ÷ rated load per tire)

rounded up — you never round a load-safety number down.

Step 1 — Load per tire

The total weight splits across the axles by your chosen distribution, tongue weight is added to the rear axle, and each axle's load divides by the number of tires on it (2 for a single-rear-wheel vehicle, 4 for a dually):

rear axle = total × rear% + tongue weight · load per tire = axle load ÷ tire count

Step 2 — Reference pressure by load range

The rated load lives at a pressure fixed by the tire's construction:

• SL (Standard Load) passenger tires — rated load at 35 PSI
• XL (Extra Load) passenger tires — rated load at 41 PSI
• LT Load Range C / D / E / F — rated load at 50 / 65 / 80 / 95 PSI

Step 3 — Rated load from the load index

The load index maps to a rated load in kilograms (an ISO/Tire & Rim Association standard); we convert to pounds. Load index 100 = 800 kg = 1,764 lb per tire; 121 = 1,450 kg = 3,197 lb. Scale the reference pressure by how much of that rated load each tire actually carries, and you have the minimum cold pressure.

The number is a floor, not a ceiling

The result is the minimum cold pressure to carry the load — it's most useful when you're heavy. A lightly-loaded car on high-capacity tires will compute a low number you'd never street-drive, because handling, heat, and wear all want more air than the bare load minimum. For everyday driving, set the higher of this number and your door-placard spec. When you're loaded or towing and the calculated number climbs past the placard, that's the number that matters.

Three worked examples

F-150 towing a travel trailer

6,000 lb loaded, 48/52 split, 700 lb of tongue weight, on XL tires with load index 116 (2,756 lb/tire). The rear axle carries 3,120 + 700 = 3,820 lb, or 1,910 lb per tire — 69% of rated. Reference pressure for XL is 41 PSI, so the rear needs 29 PSI cold to carry it; the lighter front only needs 22. On the street you'd run the placard 35 front, but the calculator confirms the loaded rear is well within the tire's rating with margin to spare.

3/4-ton hauling on Load Range E

8,000 lb, balanced 50/50, load index 121 (3,197 lb/tire), Load Range E (reference 80 PSI). Each tire carries 2,000 lb — 63% of rated — so the minimum is 51 PSI cold front and rear. That's why heavy-duty trucks run 50–65 PSI empty and climb toward 80 loaded: the load genuinely needs it, and under-inflating an E-rated tire is how sidewalls fail under a load.

Lightly-loaded commuter car

3,200 lb FWD car, 60/40 split, load index 91 (1,356 lb/tire), SL tires. The front carries 960 lb/tire (71% of rated) → 25 PSI minimum; the rear only 17. Nobody drives 17 PSI — you'd run the placard 33–35 for handling and wear. This is the case where the placard wins, and the calculator shows you have enormous load headroom.

Frequently asked questions

Is this the pressure I should actually run?

It's the minimum to carry the load. For street driving, run the higher of this number and your door-placard pressure. The load-based figure becomes the number that matters when you're heavy — towing, hauling, loaded for a trip — or when you've fitted non-OE tires and the placard no longer applies. Many towing guides also add a ~5 PSI margin on the loaded axle for heat.

Where do I find my load index and load range?

Both are on the tire sidewall. The load index is the two- or three-digit number right after the size and before the speed-letter (P235/65R17 108T → 108). Load range is printed as "Standard Load" / "Extra Load" (or SL/XL) on passenger tires, or as "LOAD RANGE E" on LT tires. Our Tire Ply Rating + Load Index Chart decodes any code to its capacity in pounds.

What total weight should I enter?

For an everyday estimate, use curb weight plus passengers and cargo. For the safe worst-case, use your GVWR — the max loaded weight on the door placard. The most accurate input is a real scale weight: drive onto a CAT scale at a truck stop for per-axle numbers, then you can even skip the split estimate.

Why does it say my load is "over rating"?

Because the per-tire load exceeds what that load index can carry even at its full reference pressure. Adding air won't fix it — capacity is capped at the rated load. You need a higher load index or load range (a stronger tire). This warning exists to stop a genuinely dangerous overload, common when people put passenger-rated tires on a loaded truck.

Does this work for trailer tires?

The load-per-tire math is the same, but trailer (ST) tires are almost always run at their sidewall max pressure regardless of load — that's the standard trailer-tire practice for stability and heat. Use this calculator to confirm your ST tires' rated load covers the loaded trailer weight per tire; set the pressure to the sidewall max, not the computed minimum.

Related tools

• Recommended Tire Pressure Lookup — the door-placard PSI for 100+ stock vehicles by year/make/model.
• Tire Ply Rating + Load Index Chart — decode any load index or Load Range letter to capacity in lb/kg.
• Bar to PSI Converter — translate a European bar sticker into PSI.
• Tire Height & Diameter Calculator — check how a plus-size swap changes overall diameter.
• Browse all free tools by Mike Reeves →

Mike's recommendations for hitting your number

Knowing the load pressure only helps if you can set it accurately, cold. Three product categories cover the gap:

• Best Tire Pressure Gauges — a ±0.5 PSI digital gauge is the only way to confirm you actually hit the load number. Truck pressures run high; a cheap pencil gauge drifts most at 50–80 PSI.
• Best Portable Tire Inflators — load figures on trucks and trailers land at 50–80 PSI, where gas-station hoses stall. A cordless inflator hits the target cold in your driveway. Check the current picks on our tire inflator roundup.
• Best All-Season Tires — if the calculator says "over rating," the fix is a higher-load-index tire, not more air. Old or worn sidewalls also lose pressure faster.

Sources & methodology

• Formula: Tire & Rim Association (TRA) / ETRTO load-inflation relationship — load capacity scales with inflation pressure; rated load is defined at a type-specific reference pressure. required PSI = reference × (load ÷ rated load), rounded up.
• Reference pressures: SL 35 PSI, XL 41 PSI, LT-C 50, LT-D 65, LT-E 80, LT-F 95 (TRA / ETRTO standard load tables).
• Load index → rated load: ISO/TRA load-index table (kg), converted to pounds at 2.20462 lb/kg.
• Load-and-inflation practice: Michelin and Toyo RV/truck load-and-inflation guidance; RVSEF weigh-and-inflate method.
• Temperature drift (1 PSI / 10°F): Firestone Complete Auto Care, Bridgestone Tire School.

The load-index table and constants are in fixtures.json, verified by a CI accuracy test. About Mike Reeves · Last reviewed August 7, 2026.

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  Tire pressure calculator by
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  &middot; Reviewed by Mike Reeves, ASE Master Technician
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