P-Metric / Euro-Metric Converter

Convert between P-metric, Euro-metric, and JATMA tire standards with load rating comparison.

Introduction

The P-Metric/Euro-Metric Converter is an international standard tool that analyzes and cross-converts the subtle but important differences between various tire sizing systems used globally. While P-Metric (primarily US), Euro-Metric, and Japanese JATMA standards may look similar, they have critical differences in how load indices are calculated and how they handle load capacity at different inflation pressures. This tool clarifies these engineering distinctions for safe tire selection.

How It Works

The system databases load index tables and pressure correction factors for each standard. For example, while a 205/55R16 might look identical, P-Metric tires are rated for passenger loads, whereas Euro-Metric often handles higher pressures and loads. The converter translates not just physical dimensions (diameter, width) but also max load values (kg/lbs) using each standard's formulas, automatically applying rules like the 9% load reduction required when mounting passenger (P-Metric) tires on SUVs or trucks.

Usage Scenarios

When buying tires via international shipping or replacing stock tires on an imported vehicle, verify that the different standards don't create issues with load capacity.
If mounting high-performance European tires on an American pickup truck, use this to precisely compare load index differences between standards to ensure they can safely support the truck's weight.
For tire professionals explaining the differences between brands from different countries to customers, use this as an authoritative data source for recommending proper inflation pressures.

How to Use the P-Metric / Euro-Metric Converter

Select your tire size, load index, and speed rating to see equivalent specifications across P-metric, Euro-metric, and JATMA standards.

P-metric (used in North America) has slightly lower load capacity than Euro-metric at the same load index. JATMA (Japanese standard) may have different markings but similar physical dimensions.

The three standards use similar but not identical nominal dimensions (OD typically varies by 3–6mm); the larger practical difference is in load capacity ratings.

In-Depth Guide

Metric (mm) sizes and inch-based flotation sizes describe the same tire two ways. A 33×12.5R15 flotation tire is 33 inches (838 mm) tall and 12.5 inches (317 mm) wide on a 15-inch rim; to approximate it in metric, diameter = rim×25.4 + 2×(width×aspect/100), so a 315/75R16 (315 × 0.75 × 2 + 406.4 ≈ 879 mm ≈ 34.6 in) is a close metric analog. Converting inches to mm is simply ×25.4, and mm to inches is ÷25.4.

Standards differ in load handling even at identical dimensions. P-metric (US passenger, prefix 'P') sizes are de-rated ~9% when fitted to light trucks/SUVs, while Euro-metric (no prefix) and LT (Light Truck) sizes use different load-inflation tables and higher reference pressures. JATMA (Japan), ETRTO (Europe), and TRA (US) publish the load tables; a 205/55R16 'looks' universal but its rated kg can vary by standard. A common mistake is treating P205/55R16 and 205/55R16 as interchangeable for towing or hauling.

Aspect ratio is the only field that is a ratio rather than a length, which is why two sizes can share a width and rim yet differ wildly in diameter (215/45R17 vs 215/65R17). When a tire omits the aspect number entirely (e.g., 31×10.5R15 or older 'full profile' designations) it implies roughly an 80-92 series profile. Always confirm the actual load index and the speed symbol survive the conversion, not just the geometric diameter, since a dimensionally similar tire with a lower load index is not a safe substitute.