Is the iridium plug
actually worth the upgrade?
Iridium plugs cost 4× as much per unit as copper. They also last 3.3× longer (100K vs 30K miles) and give a small fuel-efficiency uplift (~1.2%) over a horizon. The calculator works out whether the longer life and small gas savings actually beat the upfront cost over your driving horizon, including the labour cost of fewer swaps.
plug upgrade comparison
Current plug type
Target plug type
Engine plug count
Miles per year
Vehicle MPG
Gas price ($/gal)
Labour per swap ($)
Horizon (years)
over 8 years
UPGRADE SAVES
+$314
vs continuing on Copper over 8 years
where the upgrade pays off
Plug ratings (miles to replacement): Copper 30K · Platinum 60K · Iridium 100K. Fuel-efficiency gains are modest and well-documented: +0.5% upgrading copper→platinum (cleaner combustion), +1.2% upgrading copper→iridium (smaller electrode = lower voltage = more complete burn). Iridium gains are largest in older engines with worn plugs at higher mileage. Treat numbers as upper bound; real gains depend on engine state.