Intel Core i5-8400 vs Intel Core Ultra 3 105UL Comparison

The Intel Core Ultra 3 105UL and the Intel Core i5-8400 represent two very different eras of desktop computing. The Ultra 3 is a modern, power-sipping Meteor Lake part, while the i5-8400 is a legacy Coffee Lake stalwart. The benchmark data reveals a clear generational shift, but not without a few surprising holdouts from the older chip. This analysis breaks down the head-to-head results, architectural differences, and ideal use cases for each processor.

Head-to-Head Benchmarks

The most striking pattern is the Ultra 3 105UL’s dominance in CPU-bound rendering and compute workloads. Across the entire Cinebench suite, the Ultra 3 wins every single test by a remarkably consistent margin. In Cinebench R15, it scores 881 versus 790 for the i5-8400, a 11.5% lead in multi-core and 124 versus 111 (11.7%) in single-core. This consistency carries into R20, where the Ultra 3 posts 3671 against 3295 (11.4% multi-core) and 518 against 464 (11.6% single-core). The R23 results tell the same story: 8742 versus 7847 for an 11.4% multi-core win, and 1234 versus 1107 for an 11.5% single-core victory. The data shows the Ultra 3 is uniformly about 11-12% faster in this renderer, regardless of the workload or thread count.

The gap widens significantly in PassMark’s math and encryption tests. The Ultra 3’s integer math score of 41171 crushes the i5-8400’s 25573, a massive 61% advantage. Floating-point math is similarly lopsided, with the Ultra 3 at 30750 versus 22006, a 39.7% lead. The most extreme outlier is data encryption, where the Ultra 3 scores 6354, more than double the i5-8400’s 2824 — a 125% delta. These are not marginal wins; they indicate a fundamentally more capable execution engine for modern instruction sets. Even in the single-threaded PassMark test, the Ultra 3’s 3382 score is 42.6% higher than the i5-8400’s 2371, which is a far larger single-core advantage than Cinebench suggests.

However, the i5-8400 is not without its victories. It wins three of the seventeen head-to-head tests, and they are notable. In PassMark data compression, the older chip scores 129951 versus 93961, a 27.7% win. Random string sorting also goes to the i5-8400, with a score of 15952 versus 11179, a 29.9% advantage. The third win is in extended instructions, where the i5-8400’s 11543 score is more than double the Ultra 3’s 5634, a 51.2% margin. These results suggest that while the Ultra 3 excels at raw arithmetic and encryption, the i5-8400 retains an edge in specific memory-heavy or legacy-optimized workloads. The overall benchmark score tells a different story: the Ultra 3 has an average of 13061, while the i5-8400 sits at 12765. Both chips share the same 68th percentile against all CPUs, but the average delta is in the Ultra 3’s favor.

The Verdict

The data points to a clear winner for most modern use cases: the Intel Core Ultra 3 105UL. It wins 14 of 17 benchmarks, including every Cinebench test and the vast majority of PassMark’s compute suite. Its 61% lead in integer math and 125% lead in data encryption are decisive for developers, analysts, or anyone running modern productivity software. The 42.6% single-thread advantage also makes it the better choice for everyday responsiveness and lightly-threaded applications. The Ultra 3 is also a generation ahead in efficiency, with a 15W TDP versus the i5-8400’s 65W, though the i5-8400’s higher power draw correlates with its older 14nm process.

The Intel Core i5-8400 is only the right pick for a narrow set of legacy workloads. Its 27.7% win in data compression and 29.9% win in random string sorting could matter for archival or database tasks that rely on those specific patterns. The 51.2% lead in extended instructions is harder to leverage, as this test often reflects older SIMD capabilities. For anyone building a new system or upgrading, the Ultra 3 is the safer, faster choice. The i5-8400’s strengths are too niche, and its end-of-life status means no future platform support. If your software is single-threaded or computationally intensive, the Ultra 3 is the only sensible pick from this comparison.

Architecture Differences

The two chips are built on entirely different foundations. The Intel Core Ultra 3 105UL uses the Meteor Lake architecture on a 7nm process, while the Intel Core i5-8400 is a Coffee Lake part on Intel’s older 14nm node. This process difference explains much of the power and efficiency gap: the Ultra 3 has a 15W TDP, whereas the i5-8400 is rated at 65W. The Ultra 3 also has a higher core count, with 8 cores and 10 threads, compared to the i5-8400’s 6 cores and 6 threads. This extra parallelism directly contributes to its multi-core wins.

Cache hierarchy is also distinct. The Ultra 3 has a 112 KB L1 and 2 MB L2 per core, with 10 MB of shared L3. The i5-8400 has 64 KB L1 and 256 KB L2 per core, with only 9 MB of L3. The larger per-core caches on the Ultra 3 likely help its single-thread performance, which is evident in the 42.6% PassMark single-thread win. Memory support differs as well: the Ultra 3 uses DDR5, while the i5-8400 is limited to DDR4. This is reflected in memory bandwidth, with the Ultra 3’s 89.6 GB/s nearly double the i5-8400’s 42.7 GB/s. The Ultra 3 also features Arc Xe-LPG 48EU integrated graphics, a significant step up from the i5-8400’s UHD Graphics 630.

Specification Differences

The most relevant specification differences are the core/thread counts and clock speeds. The Ultra 3 has 8 cores and 10 threads, versus 6 cores and 6 threads on the i5-8400. Despite this, the i5-8400 has a higher base clock of 2.80 GHz, while the Ultra 3 starts at 1.50 GHz. However, the Ultra 3 boosts higher, reaching 4.20 GHz compared to the i5-8400’s 4.00 GHz. The Ultra 3’s lower base clock is a trade-off for its 15W TDP, but the higher boost helps it win single-thread tests.

The sockets are incompatible: the Ultra 3 uses Intel Socket 1851, while the i5-8400 uses Intel Socket 1151. PCIe support also differs, with the Ultra 3 offering Gen 4 (8 lanes) and the i5-8400 offering Gen 3 (16 lanes). The Ultra 3 has a larger L3 cache at 10 MB versus 9 MB, and its memory bus is DDR5 compared to DDR4. The i5-8400 has a specified die size of 154 mm², while the Ultra 3’s is not listed. Both chips have no unlocked multiplier, and both lack ECC memory support. The Ultra 3 was released in 2024 and is still active, while the i5-8400 launched in 2017 and is end-of-life.

FAQ

Q: Which CPU is faster in multi-core rendering?

A: The Intel Core Ultra 3 105UL wins all Cinebench multi-core tests, with an 11.4% lead in R20 (3671 vs 3295) and an 11.4% lead in R23 (8742 vs 7847).

Q: Is the Intel Core i5-8400 better at anything?

A: Yes, it wins three benchmarks: data compression (129951 vs 93961, a 27.7% lead), random string sorting (15952 vs 11179, a 29.9% lead), and extended instructions (11543 vs 5634, a 51.2% lead).

Q: How much better is the Ultra 3 in single-threaded tasks?

A: In PassMark’s single-thread test, the Ultra 3 scores 3382 versus 2371, a 42.6% advantage. In Cinebench R23 single-core, it leads 1234 versus 1107, an 11.5% margin.

Q: What is the power consumption difference?

A: The Ultra 3 has a 15W TDP, while the i5-8400 has a 65W TDP. This is a major architectural difference reflecting the newer 7nm process.

Q: Which CPU has better integrated graphics?

A: The Ultra 3 uses Arc Xe-LPG 48EU, while the i5-8400 has UHD Graphics 630. The Ultra 3’s GPU is from a newer generation.

Q: Should I upgrade from the i5-8400 to the Ultra 3?

A: Benchmark results indicate yes for most users. The Ultra 3 wins 14 of 17 head-to-head tests, with a 61% lead in integer math and a 125% lead in data encryption. The i5-8400’s wins are niche and its end-of-life status limits future support.

Where Each One Wins

The Intel Core Ultra 3 105UL is the clear winner for any modern, compute-heavy workload. It dominates in integer math (61% ahead), floating-point math (39.7% ahead), and data encryption (125% ahead). Its consistent 11-12% lead across all Cinebench versions makes it ideal for 3D rendering, video encoding, and software compilation. The 42.6% single-thread advantage also makes it better for general desktop use, web browsing, and office applications. Gamers pairing this with a discrete GPU will benefit from the higher boost clock and faster DDR5 memory bandwidth.

The Intel Core i5-8400 has a narrow but real set of wins. Its 27.7% lead in data compression and 29.9% lead in random string sorting could make it suitable for specific data-logging or file-archival tasks. The 51.2% margin in extended instructions might help with legacy scientific software that uses older SIMD paths. However, these are not workloads the average builder targets. The i5-8400’s 16 PCIe Gen 3 lanes versus the Ultra 3’s 8 Gen 4 lanes could offer more raw bandwidth for multi-GPU setups, though Gen 4’s higher per-lane speed mitigates this. For anyone building a new PC, the Ultra 3 is the better investment; for those with an existing Socket 1151 board, the i5-8400 is still serviceable for its niche strengths.