Your TV can list HDMI 2.1 on the box and still only deliver 4K at 120Hz on one or two of its four HDMI inputs. That happens because the 2.1 label doesn’t guarantee every headline mode — the chipset behind the ports may only give full speed to a couple of lanes.
The difference is per-port bandwidth, not just the version sticker. Some inputs are built for 48Gbps and can carry 4K120 plus VRR and ALLM, while the others stay capped at the older 18Gbps ceiling for 4K60. Once you know where to find your model’s per-port table that lists Enhanced Format 4K120, you can run a 60-second same-source swap test and map which socket actually does what — here’s the matrix that makes it obvious.
Why your TV can say HDMI 2.1 and still not give you 4K at 120Hz on every port
In 2019 HDMI Licensing stopped certifying new devices as HDMI 2.0 and folded everything into HDMI 2.1. At the same time the organization made nearly all headline features optional. That means a TV can truthfully be labeled HDMI 2.1 while only implementing eARC or 4K60 modes.
HDMI 2.1 features optional explains products can no longer be certified for 2.0, only for 2.1, and 2.1 features are optional to implement, so popular features like 4K120, ALLM, and VRR are not required. A maker can claim 2.1 while only adding eARC and keep the other ports at the older speed tier.
The speed tier that matters is defined by HDMI Forum. HDMI Forum 48Gbps vs 18Gbps notes the new standard will increase link bandwidth to 48 Gbps, enabling 4K120 where the predecessor topped out at 18 Gbps. If a port’s hardware retimer only exposes 18 Gbps, no firmware update can make it negotiate 48 Gbps.
This is why one HDMI input does 4K120 on your TV while HDMI 1 does not. The fast lane exists, just not everywhere.
At the back of the TV, look for HDMI port labels printed near the sockets — eARC, 4K 120Hz, or Game — then photograph them for comparison to your manual’s per-port table. That photo is your starting point for the verification steps later.
What 18Gbps vs 48Gbps actually means for 4K 120Hz
Bandwidth is the hard ceiling. An uncompressed 4K60 8-bit 4:4:4 signal needs close to 18 Gbps. Add 10-bit color and 120Hz and the math jumps well beyond that.
18Gbps vs 48Gbps port difference states HDMI 2.0 tops out at 18 Gbps and is capable of delivering up to 4K at 60Hz, while HDMI 2.1 has a maximum of 48 Gbps that supports 4K at 120Hz. HDMI 2.1 48Gbps enables 4K120 puts it plainly: the former supports only 18 Gbps to achieve 4K at 60Hz whereas HDMI 2.1 clocks in at 48 Gbps and promises 4K at 120Hz.
bandwidth comparison table lists data bandwidth as 48 Gbps for HDMI 2.1 versus 18 Gbps for HDMI 2.0, which is the practical split between 4K60 and 4K120 capability.
A TV maker limits fast ports to save cost. A full 48 Gbps retimer, signal integrity design, and certification for four lanes costs more than wiring two fast lanes and two slower 18 Gbps lanes for streaming sticks that never need more than 4K60.
If 4K120 4:4:4 10-bit needs roughly 32 to 40 Gbps estimated depending on chroma and blanking, 18 Gbps can never carry it, even with a better cable. That’s the mechanism behind why moving the same console and cable to another port changes the result.
How manufacturers split those bandwidth lanes across the four ports
Most mid-range TVs from 2021 to 2023 ship with two full-bandwidth ports and two limited ones. Higher-end models like LG C3 or Samsung S90C wire all four for 48 Gbps.
Sony’s documentation is a clear example of the labeling pattern, not a claim about all Sony TVs. Sony’s own support article lists Sony per-port feature table showing features specified in HDMI 2.1 as 4K120, eARC, VRR, ALLM, and marks Variable Refresh Rate as Yes for HDMI 3 and 4 only. The US version repeats Sony HDMI 3/4 4K120 VRR — HDMI signal format Enhanced format 4K120 VRR, HDMI 3 and 4 VRR only.
By contrast, current-generation flagship sets from LG and Samsung typically ship with four full-bandwidth HDMI 2.1 ports — LG’s OLED C-series lines have offered four 48 Gbps ports with 4K at 120Hz VRR on all four since the C3 generation, and Samsung’s gaming-focused sets have matched that with four HDMI 2.1 4K120 inputs on all ports.
In Reddit r/bravia and Sony Community, owners described a PC connected to HDMI 4 which supports 4K120 losing audio when VRR was enabled, while audio on other inputs continued, requiring a VRR toggle to restore even with a certified 4K120 cable. The solution that came up repeatedly was ensuring HDMI signal format was set to Enhanced format VRR on HDMI 3 and 4, using an Ultra High Speed cable, and enabling eARC mode Auto to stabilize the handshake, which works because those two ports are the only ones with the 48 Gbps lane needed for 4K120 VRR while HDMI 1 and 2 remain capped at 18 Gbps per the HDMI Forum 48Gbps vs 18Gbps tier definition.
Stage boxes showing game console 4K120 48Gbps output entering TV internal switch with two ports labeled full bandwidth 48Gbps supporting 4K120 VRR and two ports labeled limited bandwidth 18Gbps capped at 4K60
The ARC vs eARC bandwidth story in our guide on soundbar Atmos over HDMI explains why eARC shares the same 48 Gbps requirement discussion — it’s a complementary example of optional-feature allocation, not a repeat of this port test.
How to check your model’s per-port feature table and confirm bandwidth
You need your exact model number and the same cable moved port to port. No app can guess bandwidth for you.
First, find the model label on the back. Open the manufacturer’s spec PDF and search for HDMI signal format or Features specified in HDMI 2.1. HDMI signal format menu shows HDMI signal format Enhanced format 4K120 and Enhanced Format VRR depending on model — that line is your per-port truth table.
Second, open the TV menu. On many TVs it’s Settings > External inputs > HDMI signal format. You should see options like Standard, Enhanced, Enhanced format 4K120, Enhanced format VRR. HDMI format menu check advises to comb through menus and look for HDMI format setting and check whether a port supports Enhanced Formats VRR ALLM 4K120Hz — if it does, it’s an HDMI 2.1 capable port.
Third, run the reproducible test. Use one Ultra High Speed cable under 2 meters and one source set to 4K120 — PS5 Performance Mode 120Hz enabled, Xbox Allow 4K and 120Hz checked, or PC set to 3840×2160 120Hz in display settings. Plug into HDMI 1, record what the TV info banner and console report. Repeat for HDMI 2, 3, and 4 with the same cable and source. That log is your matrix.
Before committing, move the same console and same certified cable to HDMI 1, then 2, then 3, then 4, and write down what refresh the console offers and what the TV info banner reports each time — that log is your per-port matrix. It takes a minute.
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Checklist of four steps to identify fast ports with result area showing which ports passed 4K120 negotiation
Compatibility matrix — where to plug your console, PC, soundbar, and streaming stick
Your log from the previous section now tells you which inputs are 18 Gbps and which are 48 Gbps. This matrix is a practical tool built from that bandwidth mechanism to decide placement, not a published industry standard.
Logic: consoles and PC GPUs that need 4K120 VRR ALLM get the fast ports first. Soundbars need the eARC port, which on many TVs is also one of the fast ports, usually HDMI 3. Streaming sticks like Apple TV 4K or Fire TV Max do fine on the 18 Gbps ports because they rarely need more than 4K60.
populate fast ports first advises to populate HDMI 2.1 ports first especially if you own a current-gen console or PC because HDMI 2.1 supports 4K120Hz, while streaming boxes can work fine over HDMI 2.0. The best current gaming TVs generally list four HDMI 2.1 ports offering 4K 120Hz VRR to take full advantage of a PS5 or Series X — the opposite allocation from budget models.
| Device type | 18Gbps 4K60 port | 48Gbps 4K120+VRR+ALLM port |
|---|---|---|
| PS5 / Xbox | Capped at 4K60 est. | Recommended — 4K120 VRR est. |
| PC GPU | No 120Hz + VRR flicker risk | Recommended — full bandwidth |
| Soundbar eARC | No eARC audio return | Use HDMI 3 eARC port est. |
| Streaming stick | Fine here — saves fast port | Works but wastes fast lane |
Comparison table with device types as rows and port types as columns showing recommended placement and what happens if placed on slow port
This rubric is a practical evaluation tool created for this guide based on per-port bandwidth allocation and optional-feature status described above, not a published industry standard. Use it as an in-home quick-check.
Why VRR and ALLM also only work on the fast ports
VRR and ALLM are part of the same optional HDMI 2.1 feature set as 4K120. They need the same Enhanced signal format mode.
HDMI 2.1 VRR ALLM features lists HDMI 2.1 spec as including Variable Refresh Rate VRR and Auto Low Latency Mode ALLM alongside 48 Gbps. That means a TV can support eARC but still not expose VRR on every input.
On Sony-type models, VRR only on HDMI 3 4 explains Enhanced format VRR option exists only on HDMI 3 and HDMI 4, so you must connect a gaming console to that specific port to use VRR. If you plug a PS5 into HDMI 1 set to Standard format, VRR stays greyed out because the port never enters the 48 Gbps mode that carries VRR metadata.
In an RTINGS discussion, users reported using HDMI port 4 with an RTX 3000 series at 4K120 VRR causing flickering and loss of sync especially in Game mode. The pattern that reduced flicker was setting TV HDMI signal format to Enhanced VRR and ensuring an Ultra High Speed cable under 2 meters plus disabling other HDMI devices, which aligns with why VRR requires the same 48 Gbps Enhanced format path as 4K120 and fails on 18 Gbps ports per HDMI Forum bandwidth tiers.
Why buying another 4k 120hz cable doesn’t fix a slow port
An Ultra High Speed cable can carry 48 Gbps, but it can’t make an 18 Gbps port negotiate faster. The port’s retimer and chipset lane are the ceiling.
It feels reasonable because the cable package says 4K120. It fails because the bottleneck is silicon, not copper. cable plus port both needed notes you won’t enjoy HDMI 2.1 benefits if you use the wrong HDMI cable, but you also need the 2.1 port itself. cable and TV both must support feature adds that an HDMI 2.1 TV or cable may not support everything a shopper thinks, because manufacturers can implement only a subset.
If your test showed HDMI 1 and 2 capped at 4K60 even with the same certified cable that does 4K120 in HDMI 3, stop buying cables. Move the 4K120 device to the fast port or add a certified HDMI 2.1 switch that maintains 48 Gbps end to end.
What to verify first
Move your console and PC to the ports labeled 4K120 or Game and check the manual line that says Features specified in HDMI 2.1 4K120 VRR ALLM to confirm which inputs are actually full speed. Open Settings, set that port’s HDMI signal format to Enhanced format 4K120 or Enhanced format VRR, and log what each input negotiates with the same Ultra High Speed cable. Skip that matrix and you’ll keep swapping cables thinking one is faulty while your console sits on an 18 Gbps input capped at 60Hz.
Frequently Asked Questions
Which hdmi port is 4k 120hz on my tv?
Look for a back-panel label like 4K 120Hz, Game, or eARC and check the manual for Features specified in HDMI 2.1 4K120. Sony per-port table shows HDMI 3 and 4 as 4K120 VRR Yes, while other TVs list all four as full bandwidth.
Why does my tv say hdmi 2.1 but i can’t get 4k 120hz?
The HDMI LA allows the 2.1 label even if only eARC or 18 Gbps modes are implemented because features are optional. HDMI 2.1 optional features explains 4K120, VRR, and ALLM aren’t required to claim 2.1, so you still need a 48 Gbps port.
Does hdmi 2.0 support 4k 120hz with a better cable?
No. 18 Gbps is the ceiling for HDMI 2.0 and can’t carry 4K120 4:4:4 even with an Ultra High Speed cable. The bandwidth ceiling difference is 48 Gbps vs 18 Gbps — the difference between 4K144 and 4K60 common peaks.
My ps5 shows 4k 60hz only — is it the cable or the port?
Test the same cable in HDMI 3 or 4. If the PS5 offers 120Hz there but not in HDMI 1 or 2, it’s the port bandwidth, not the cable. Also set TV to Enhanced format and PS5 Video Output to 120Hz Auto.
