Car Tire Size / Car battery size / Group 121R
Group 121R battery size
A group 121R car battery is at most 8.19 inches long, 6.97 wide and 8.46 tall (208 x 177 x 215 mm), with top posts.
- Length
- 8.19 in (208 mm)
- Width
- 6.97 in (177 mm)
- Height
- 8.46 in (215 mm)
- Terminals
- top posts
Close in size
Groups within 10 mm (0.4 in) on every side:
- Group 21: 8.19 x 6.81 x 8.74 in, different terminal layout (BCI figure 10, not 11H).
- Group 21R: 8.19 x 6.81 x 8.74 in, different terminal layout (BCI figure 11, not 11H).
Before you buy a group 121R battery
- Read the group number on the label of the battery in your car, or in the owner's manual: it should say 121R.
- The "R" means the terminals are reversed compared with the same number without R: the positive post is on the other side.
- Choose cold cranking amps (CCA) at least as high as the original, especially for cold winters.
- Group 121R has top posts: the new battery must match, and the hold-down must fit the box.
- Most stores take the old battery back for recycling, often against a core charge.
Group 121R batteries listed on eBay
Dimensions are the BCI maximums for the case, terminals excluded. Sources: Battery Council International, "BCI Group Numbers, Dimensional Specifications and Ratings" (batterycouncil.org), read October 15, 2026; Power Tool Insider, "Car Battery Group Size Chart" (powertoolsinsider.com), updated October 7, 2026.