TERM-TOTAL-BASE-NUMBER
Total Base Number
Lubrication
Also: TBN · base number · alkalinity reserve · reserve alkalinity
Abbrev: TBN · BN
Canonical Definition
A measure of an oil's reserve alkalinity — its capacity to neutralise acids formed by combustion blow-by gases and oil oxidation products. Expressed in milligrams of potassium hydroxide per gram of oil (mg KOH/g). Fresh engine oil typically has TBN of 8–14 mg KOH/g. Acidic products (sulfuric acid from combustion of sulfur-containing fuels, carboxylic acids from oil oxidation) are neutralised by alkaline additives (calcium and magnesium detergents). Oil change is indicated when TBN falls to approximately 2 mg KOH/g, below which corrosion of bearing surfaces by unchecked acid products accelerates.
Engineering Context
TBN monitoring via oil analysis is the definitive method for determining engine lube oil condition-based drain intervals. An oil maintaining high TBN is not depleted regardless of calendar time; an oil with low TBN is depleted regardless of hours. Fuel sulfur content strongly determines TBN depletion rate — high-sulfur fuels require more alkaline reserve or shorter drain intervals.
Related Technologies
Protection Systems
Knowledge Center Articles
KC-00 Governance Metadata
| Permanent ID | TERM-TOTAL-BASE-NUMBER |
| Category | Lubrication |
| Status | Published |
| Version | 1.0 |
| Last Reviewed | 2026-07-05 |