Car Battery Size Chart & Group Size Finder
Every 12-volt car battery carries a BCI group size - a code like 24F, 35, or 48/H6 that fixes its physical dimensions and terminal layout. Pick the wrong group and the battery will not fit the tray, the cables will not reach, or the hold-down will not clamp. This page gives you the full group-size chart (19 common groups, inches and mm), a vehicle finder, a tray-fit checker, and a terminal-orientation guide.
Which group size fits your vehicle?
BCI group size chart (click a header to sort; dimensions in inches)
| Group | L × W × H | Typical CCA | Terminals | Common applications |
|---|
Dimensions are maximum BCI dimensions (L × W × H). "Typical CCA" is representative of common models - CCA is model-specific and is not set by the group number.
Will it fit your tray?
Measure the inside of the battery tray (or the old battery) and enter the three dimensions. The checker lists every standard group that fits.
Compare two group sizes
Terminal orientation: the 10-second check
Stand the battery so the terminals face you (closest edge). On a standard group, the positive (+) post is on the left. On an F or R group (24F, 34R, 51R, 94R), the positive post is on the right.
Top post vs side terminal
Most groups use tapered top posts (SAE). Groups 75 (9.06 x 7.06 x 7.31) and 78 (10.25 x 7.06 x 7.31) use side terminals - threaded sockets on the side of the case, common on older GM vehicles. The two systems need different cable ends and are not interchangeable without adapters.
How to read a battery label
A typical top label shows three things you actually need: the group size ("Group 35", "H6", "95R"), the CCA rating ("640 CCA"), and sometimes the reserve capacity ("100 min"). The group size answers "will it fit", the CCA answers "will it start my engine in winter", and the reserve capacity answers "how long will it run the electrics with the engine off". Brand and warranty sit underneath - useful, but they do not change the physical fit.
What a BCI group size actually guarantees
The Battery Council International assigns each group number a set of maximum dimensions and a terminal layout. That is the entire guarantee: any Group 35 on any shelf is 9.06 x 6.94 x 8.88 in or smaller, with top posts in the standard position. Everything else - CCA, reserve capacity, chemistry (flooded, EFB, AGM), warranty - varies by brand and model line. This is why the chart lists typical CCA rather than a standard: there is no standard CCA per group.
CCA, CA, and reserve capacity - plain English
CCA (cold cranking amps) is the current a battery can deliver for 30 seconds at -18°C (0°F) while staying above 7.2 V. It is the number that matters for winter starting. CA (cranking amps) is the same test at 0°C (32°F), so the number looks bigger - roughly 1.25× the CCA - but means the same thing measured warm. Reserve capacity is how many minutes the battery can deliver 25 A before dropping to 10.5 V; it matters if your alternator fails or you run accessories with the engine off.
Rule of thumb: match your climate, not your ego. In a mild climate the typical CCA for your group is plenty. For regular frosts, buy about 20 percent more CCA than the baseline; for winters below -18°C, buy the highest-CCA model in the group and prefer AGM. More CCA than that buys you almost nothing except a heavier receipt.
Start-stop cars: same size, different chemistry
If your car has automatic start-stop, the group size is the same as the conventional version of that car - but the battery must be EFB or AGM. Start-stop micro-cycling kills a standard flooded battery within months. If the factory battery is AGM, replace it with AGM: the charging system is calibrated for AGM charge voltages, and many European cars also need a battery registration procedure after replacement.
Worked examples
Example 1 - 2019 Honda Civic: which group?
A Civic is a compact car from a Japanese make. The finder recommends Group 51R first, with Group 35 as the alternative. Group 51R measures 9.38 x 5.06 x 8.75 in (238 x 129 x 223 mm) L × W × H, with a typical 500 CCA and reversed top posts (the R suffix). Check: the old battery's label says "51R", the positive cable is on the right when the terminals face you - match confirmed.
Example 2 - measuring a tray: 11.5 × 7.0 × 8.0 in
Enter those three numbers in the tray-fit checker: 5 groups fit. Group 48/H6 (11 x 6.94 x 7.5 in) fits with room to spare, so it is the natural pick - larger case, more reserve. Group 94R/H7 (12.44 x 6.94 x 7.5 in) does not fit: at 12.44 in long it overhangs the 11.5 in tray by nearly an inch, and the hold-down cannot clamp it.
Example 3 - can a Group 24 replace a Group 27?
Compare the two: Group 27 is 1.81 in (46 mm) longer than Group 24, with identical width and height. So a Group 24 drops into a Group 27 tray (shorter is fine, clamp it snugly), but a Group 27 will not fit a tray built for Group 24. You lose some reserve capacity going smaller - an acceptable trade in an emergency, not as a permanent downgrade.
Practical tips before you buy
Photograph the old battery before you remove it - label, terminal positions, and cable routing in one picture. Measure twice: length, width, and height to the underside of the hood. Check polarity with the terminals-facing-you test from the terminal guide; F/R suffix mistakes are the number one wrong-battery return. Confirm the hold-down: top-bar clamps need the right height, base-lip clamps (H-series) need the lip. Check the date code on the shelf battery - anything older than 6 months deserves a fresher one. Trunk-mounted batteries (many BMW/Mercedes) need a vent tube; make sure the replacement has the vent port.
Frequently asked questions
What battery group size do I need for my car?
Use the finder above: pick your vehicle class and the make's origin. For example, a compact Japanese car like a Honda Civic typically takes Group 51R (9.38 x 5.06 x 8.75 in). The surest check is still the label on your old battery or the owner's manual, because some trims use a different group than the class default.
What do battery group numbers like 24F, 35, or 48 actually mean?
They are BCI (Battery Council International) size codes. The number fixes the battery's maximum physical dimensions and terminal layout - Group 35, for instance, is 9.06 x 6.94 x 8.88 in. The code says nothing about brand or quality; any two Group 35 batteries are the same physical size by definition.
What does the F or R at the end of a group size mean?
It means reversed terminal polarity. A 24F has the same case as a Group 24 but the positive post sits on the opposite side. Buy the wrong one and your cables will not reach - or worse, you will be tempted to stretch them across the battery, which is a short-circuit risk.
What are H5, H6, H7, and H8 batteries?
Those are DIN/EN labels for the same physical sizes as BCI Groups 47, 48, 94R, and 49. Group 48/H6, for example, is 11 x 6.94 x 7.5 in. European cars usually print the H label; US parts stores usually print the BCI number. They are interchangeable when the dimensions match.
Does a bigger group size mean more CCA?
Not automatically. CCA is set by the battery's internal design, not its group number - one brand's Group 24 may be rated 650 CCA and another's 800 CCA. Group size guarantees fit; CCA is a separate spec you choose for your climate. The chart's 'typical CCA' column is a representative value, not a standard.
How much CCA do I actually need?
In a mild climate, the typical CCA for your group is fine. For cold winters, choose at least 20 percent more than the baseline; below -18 C / 0 F, pick the highest-CCA model in the group and prefer AGM. A battery loses roughly a third of its cranking power at 0 F while the engine needs more of it, so winter is when weak CCA shows up.
Can I use a different group size than the manual specifies?
Sometimes, with care. The replacement must fit the tray, clear the hood, match the terminal type and polarity, and be clampable by the hold-down. A shorter battery in a longer tray (Group 24 in a Group 27 tray) usually works; the reverse does not, because Group 27 is 1.81 in (46 mm) longer. Never compromise on terminal polarity.
How do I measure my battery tray?
Measure the inside of the tray or the old battery: length (longest side), width, then height to the underside of the hood or hold-down bar. Enter the three numbers in the tray-fit checker above. Leave about 1/2 in (13 mm) of clearance for cables and the clamp - for example, a 11 x 6.94 x 7.5 in Group 48/H6 fits an 11.5 x 7.0 x 8.0 in tray, while a 12.44 x 6.94 x 7.5 in Group 94R/H7 does not.
What is the difference between top-post and side-terminal batteries?
Top-post batteries (most groups) have tapered SAE posts on top; side-terminal batteries (Groups 75 and 78, common on older GM vehicles) have threaded terminals on the side of the case. You cannot swap between them without changing cable ends, and side-terminal cables are short, so measure reach before buying.
Do start-stop cars need a special group size?
The group size is the same as the non-start-stop version of the car, but the chemistry must be EFB or AGM - a standard flooded battery will fail within months under start-stop micro-cycling. If your car came with AGM, replace it with AGM; the charging system is calibrated for it.
How long does a car battery last, and does size matter?
Typically 3 to 5 years for flooded and 4 to 7 for AGM, depending on heat and use - not on group size. A larger group does not last longer; it just stores more energy. Heat is the main killer, which is why batteries in hot climates often die a year earlier.
Where is the group size printed on the battery?
On the top label, usually near the CCA rating - look for 'Group 24F', 'H6', '95R', or a BCI number in the model code. If the label is unreadable, measure the case and match it against the 19-group chart above, then confirm terminal polarity before you buy.
Dimension data: BCI group maximum dimensions cross-checked against the BatterySharks BCI group list, BatteryEquivalents per-group specification pages, and Caterpillar / MotoMaster published spec sheets (all agree on the values in this chart). CCA figures are representative of common models, not BCI standards. This is a fitment guide, not a substitute for your owner's manual.
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