Core i5-8400 — Specs, Rank & Tuning
Intel Core i5 · Coffee Lake · 2017 · Mainstream (tier 47/100)
Core i5-8400 — key specifications
| Brand / series | Intel Core i5 |
|---|---|
| Architecture / class | Coffee Lake |
| Launch year | 2017 |
| Cores / threads | 6 / 6 |
| Base / boost clock | 2.8 / 4 GHz |
| L3 cache | 9 MB |
| Socket | LGA1151v2 |
| TDP | 65 W |
| Relative tier | 47/100 — Mainstream |
Specs: vendor datasheets / TechPowerUp database, retrieved 2026-08-29. Tier is a TweakGearPro relative performance index (estimate), not a benchmark guarantee.
Relative performance estimate
TweakGearPro anchors the cpu category to its flagship (highest tier) and expresses Core i5-8400 as an estimated percentage of that flagship, derived from the relative-performance index (tier 0–100). Planning estimate, not a benchmark.
| CPU (nearby tier) | Tier /100 | Est. relative perf. |
|---|---|---|
| Core i9-9900K | 59 | 59% |
| Core i5-11400 | 58 | 58% |
| Ryzen 7 2700X | 58 | 58% |
| Core i5-10400 | 55 | 55% |
| Ryzen 7 1800X | 55 | 55% |
| Core i7-8700K | 54 | 54% |
| Ryzen 7 1700 | 52 | 52% |
Method: relative performance % = (part tier ÷ flagship tier) × 100, using the TweakGearPro tier index built from public benchmark / spec-class data. Source: vendor datasheets / TechPowerUp database, retrieved 2026-08-29. Real-world performance varies by workload, drivers and cooling.
Build compatibility & pairing guidance
Practical build notes derived from this part's dataset fields and TweakGearPro reference constants. Planning guidance, not purchase advice.
| Motherboard socket | LGA1151v2 — pair with a board that lists this socket. |
|---|---|
| Estimated system PSU | ≈ 350 W (this part's 65 W TDP + ~200 W system overhead, with 20% headroom). Confirm with the PSU Wattage Calculator. |
| Cooler / thermal | Plan cooling rated above this part's 65 W TDP; typical desktop safe ceiling is ~90°C (TweakGearPro reference). Check the Thermal Headroom tool. |
| Pairing balance | Match with a GPU whose tier is within ~20 of this part's tier (47/100) to avoid a bottleneck. Run the Bottleneck Estimator. |
Reference constants (PSU headroom 20%, safe CPU/GPU ceiling 90°C) from the TweakGearPro PC reference dataset, retrieved 2026-08-29. Adapter/case clearance and exact board power vary by model — verify with vendor datasheets.
Tune & power-plan your build
Input your cooling, case airflow and goal to generate a printable tuning sheet, or size your whole-system PSU.
Silicon-level tuning sheet
Estimates from typical thermal behavior — always verify with your own stress tests.
My Core i5-8400 tuning sheet
Air cooler: modest OC is fine; consider an undervolt first for better sustained clocks.
Stability checklist
- Record your current temps at load (HWiNFO or the vendor tool) as the baseline.
- Apply a +0.06 V voltage offset in BIOS/Afterburner (overclock).
- Test with a 10-minute stress run (OCCT / Cinebench for CPU, FurMark/3DMark for GPU) — stop if temps exceed 90 °C.
- Expected sustained clock change: +16.1% (estimate).
- If unstable, step the offset back by half and retest; stability wins over a few hundred MHz.
- Re-check after driver updates — reapply and re-verify.
Generated at TweakGearPro · 2026-09-13
Whole-system power plan
Typical board-power sums; exact figures vary by model and workload.
My power plan — Core i5-8400
PSUs are most efficient at 50–70% load. For transient GPU spikes, choose a quality 80 PLUS Gold+ unit. Generated at TweakGearPro · 2026-09-13
Release & generational notes
Core i5-8400 launched in 2017 on the Coffee Lake architecture as part of the Core i5 family, sitting at tier 47/100 (Mainstream).
| Series | Core i5 |
|---|---|
| Architecture | Coffee Lake |
| Launch year | 2017 |
| Predecessor | Core i5-6500 (2015, tier 38/100) |
| Successor | Core i5-10400 (2020, tier 55/100) |
In the Core i5 series
Core i5-2500K
2011 · Sandy Bridge · tier 26/100
Open →Core i5-3570K
2012 · Ivy Bridge · tier 31/100
Open →Core i5-4670K
2013 · Haswell · tier 35/100
Open →Core i5-6500
2015 · Skylake · tier 38/100
Open →Core i5-10400
2020 · Comet Lake · tier 55/100
Open →Core i5-11400
2021 · Rocket Lake · tier 58/100
Open →Core i5-12600K
2021 · Alder Lake · tier 74/100
Open →Core i5-12400
2022 · Alder Lake · tier 68/100
Open →Core i5-13600K
2022 · Raptor Lake · tier 84/100
Open →Core i5-13400
2023 · Raptor Lake · tier 76/100
Open →Core i5-14600K
2023 · Raptor Lake Refresh · tier 86/100
Open →Generational context is summarized from official release year and architecture only; TweakGearPro does not invent patch or refresh dates. For the full generational ranking, see the CPU Tier List.
Related hardware to compare
Same-tier peers plus a pairing from another category — open any profile.
Sources & methodology
- Specifications: vendor datasheets (NVIDIA, AMD, Intel, Samsung, WD, Crucial, Corsair, Seagate, Noctua, ASUS, LG, Dell and others) and the TechPowerUp database, retrieved 2026-08-29.
- Relative-performance index: TweakGearPro estimate built from public benchmark / spec-class data; flagship-anchored percentages are planning estimates, not measured scores.
- Reference constants (PSU headroom, safe thermal ceiling) from the TweakGearPro PC reference dataset, retrieved 2026-08-29.
- Tuning, PSU and VRAM figures are planning estimates — verify with your own stress tests and the component vendor's documentation.
How this page's estimates are computed
The relative-performance percentage anchors the category flagship (highest tier) at 100 and scales each part by its tier ratio. The estimated system PSU adds a base system overhead to the part's TDP and applies a 20% headroom from the reference dataset, rounded to a common PSU rating. The tuning sheet estimates load temperature from TDP, cooling class and case airflow, then suggests a voltage offset and expected clock delta — always confirm with a stress test. The LLM planner converts model parameters and quantization to an approximate VRAM footprint (weights + KV-cache) and divides by the card's usable VRAM to suggest a card count. None of these outputs are benchmark guarantees. For non-CPU/GPU parts the tier reflects the part's spec class relative to the best current model in that category.