Copper vs platinum vs iridium spark plugs
Copper is the cheapest plug in the box. Iridium wins on cost per mile because you replace it three times less often. Here is the math nobody else publishes, plus when to actually run each tier.
Cost per 100k miles, including shop labor
Assume a 4-cylinder engine, $120 per hour shop labor, half an hour per visit, and retail plug pricing. Tools cost is excluded so this is the shop-only comparison.
Copper
Platinum
Iridium
Copper costs roughly $250 to $440 more per 100k miles than iridium, once you include the labor for the extra shop visits. The cost-per-plug headline is misleading. Iridium and ruthenium are the cheapest tiers if you pay a shop. Copper only wins if you DIY a high-performance engine that demands its conductivity and you change plugs as a routine you enjoy.
Plain-English pros and cons of each tier
Copper
melt 1,085°C- +Best electrical conductor of the four
- +Cheapest plug in the box
- +Specified on a few high-performance and older engines
- −Softest tip, wears 3x faster than iridium
- −Wider tip means a bigger spark voltage demand
- −Triples the number of shop visits over the same mileage
Platinum
melt 1,768°C- +Middle-of-the-road durability and price
- +Hot enough to resist fouling on long highway use
- +Common factory spec on mid-2000s vehicles
- −Slightly less efficient spark than copper or iridium
- −Outclassed by iridium on cost-per-mile in 2026
- −Single-platinum vs double-platinum can confuse buyers
Iridium
melt 2,446°C- +Hardest of the common materials, finest electrode tip
- +Lowest spark voltage demand, easiest on the coil
- +Lasts 80k to 100k miles on most modern engines
- −Highest sticker price per plug
- −Brittle if dropped, replace if a new plug ever hits the floor
- −Some parts catalogs misuse the iridium label, double check
Ruthenium
melt 2,334°C- +Newer alloy, marketed as tougher than iridium under turbo or high-load engines
- +Same install procedure and torque spec as iridium
- +Available from major brands as a premium tier
- −Less aftermarket history than iridium, durability claims are not yet proven over a million-mile sample
- −Slightly higher price than entry-level iridium
- −Limited fitment outside common modern engines
Recommended plug type by vehicle
| Vehicle | Spec | Note |
|---|---|---|
| Honda Civic 1.5T | Iridium long-life | Stock from factory, do not downgrade. |
| Toyota Camry 2.5L | Iridium long-life | 100k interval is realistic, plan around it. |
| Ford F-150 EcoBoost | Iridium (gap-set, do not re-gap) | Many EcoBoost plugs ship pre-gapped, check the box. |
| Subaru WRX (turbo) | Iridium one heat range cooler | Tuned cars often run a colder plug, follow the tune. |
| Ram Hemi 5.7L | Iridium (16 plugs) | Two plugs per cylinder, parts cost is doubled. |
| BMW N54 / N55 | OEM iridium | Stay on OEM, gap is critical for direct-injection turbo. |
| Older Chevy LS V8 (build under 2007) | Platinum or iridium | Copper still works on stock LS engines, but iridium is a low-cost upgrade. |
| Race / track-only build | Copper, one heat range cooler | High RPM and boost favor copper. Replace often. |
Always cross-check the door sticker, owner manual, or VIN-keyed parts catalog. The wrong heat range or plug length will run badly even if the threads fit.
Ruthenium HX, briefly
Ruthenium plugs (NGK Ruthenium HX is the most common product line) hit the aftermarket from 2020 onward. The pitch is a slightly tougher electrode under high load, particularly on direct-injection turbo engines that demand a strong spark and stress the tip with detonation pressure. Pricing is in the same range as premium iridium. Real-world durability data is still thin, but early feedback is solid. If your vehicle is OEM-iridium, ruthenium is a valid upgrade. If you have a copper or platinum factory spec, there is no payoff in switching to ruthenium.