8BitDo Retro18 Numpad vs MMD KM21 Ultra
Choose the 8BitDo for its built-in calculator and display, or the MMD for four clickable knobs and QMK/VIA remapping.
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Which one should you get?
Get the
8BitDo Retro18 Numpad
Battery
Build quality in the top 45% of Numpad boards under $100.
- Switches between PC numpad and standard calculator modes with one click.
- Includes a dedicated shortcut button for the Windows Calculator app.
- Has a 9-digit 7-segment display.
Get the
MMD KM21 Ultra
Knob
Build quality in the top 15% of Numpad boards under $100.
- Four clickable knobs add physical controls alongside 17 hot-swappable keys.
- QMK and VIA support enable key and knob configuration.
- The CNC-milled aluminum case is paired with PORON, IXPE, and PET plate layers and bottom foam.
Pick the 8BitDo Retro18 if you want a dedicated calculator mode, a calculator shortcut, and a display in a compact numpad. Choose the MMD KM21 Ultra if configurable knobs and QMK/VIA support matter more, especially for macros or creative controls. Both are hot-swappable and support Bluetooth, 2.4 GHz, and wired use.
The differences that matter
Skip the 40-row spec sheet. These are the specs that change how each board feels, sounds, and fits your desk.
8BitDo Retro18 Numpad
MMD KM21 Ultra
Battery
1,000 mAh
980 mAh
A larger battery means fewer cables during the day
Case material
Aluminum, Plastic
Aluminum
Knob
No
Yes
Display
Yes
None
A case display rather than a typing feature
QMK
No
Yes
The deep option when you want to remap every key
- 8BitDo Retro18 Numpad
- MMD KM21 Ultra
- Performance
- 5366
- Build quality
- 6981
- Productivity
- 4989
- Customizability
- 5089
- Portability
- 8385
- Layout size: Numpad
- Connection: Bluetooth, 2.4 GHz, Wired
- Hot-swappable
- Mount style: Top Mount
What will you mostly use it for?
The KM21 Ultra has the edge for configurable workflows, gaming shortcuts, programming, and content creation, primarily because it pairs QMK/VIA with four clickable knobs. The Retro18 is the more clearly documented travel choice because its weight and dimensions are listed, and its calculator functions serve a distinct office need. Office use is a close call: one has dedicated calculator functions, the other offers remappable controls. Both provide three connection options and hot-swappable keys.
Pick the MMD KM21 Ultra
- The KM21 Ultra supports QMK and VIA, allowing keys and knobs to be configured for shortcuts.
- It has four clickable knobs in addition to its 17 hot-swappable keys.
- The 8BitDo supports N-key rollover, but its vendor description emphasizes calculator and numpad modes.
8BitDo Retro18 Numpad vs MMD KM21 Ultra specs
Every tracked spec, side by side. Rows marked with a dot differ between the boards.
11 of 22 specs differ
8BitDo Retro18 Numpad
MMD KM21 Ultra
Hot-swappable
Mount style
Sound dampening
Layout size
Layout standard
Ergonomics
Knob
Display
Connection
Battery
USB-C
Case material
Plate material
Keycaps
Weight
Dimensions
Backlight
QMK
VIA
N-key rollover
Mac & Windows
Released
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8BitDo Retro18 Numpad vs MMD KM21 Ultra: your questions
The Retro18 combines a numpad with a standard calculator mode, a Windows Calculator shortcut, and a 9-digit display. The KM21 Ultra instead adds four clickable knobs and QMK/VIA support for configurable controls.
Yes. Its vendor description says it switches between PC numpad mode and standard calculator mode with one click. It also has a dedicated shortcut button for the Windows Calculator app.
The KM21 Ultra has four clickable knobs, and its vendor description says they can be freely assigned through VIA. Suggested uses include volume, zoom, scrolling, and timeline scrubbing.
The MMD KM21 Ultra is listed with QMK and VIA support. The Retro18 vendor description mentions 8BitDo Ultimate Software V2 for firmware updates only.
Yes, both are listed as hot-swappable. The KM21 Ultra vendor description says its switches can be changed without soldering.
Both support Bluetooth and 2.4 GHz wireless, as well as wired USB-C connectivity. The Retro18 vendor description specifies Bluetooth 5.0 and says it connects without a driver.
The 8BitDo Retro18 has a screen, and its vendor description identifies it as a 9-digit 7-segment display. The MMD KM21 Ultra is listed without a screen.
Yes, the KM21 Ultra is listed with RGB lighting, and its vendor page describes RGB backlighting. The Retro18 is listed without RGB.
The Retro18 has a listed weight of 300g and dimensions of 46 x 104 x 170 mm. The KM21 Ultra's weight and dimensions are not listed here, so a direct portability comparison is not possible.
The KM21 Ultra vendor description says it comes with preinstalled MMD Cream linear switches and keycaps. Its sockets are hot-swappable for switch changes without soldering.
The KM21 Ultra is the more directly suited option because its four clickable knobs can be assigned to functions such as timeline scrubbing, zoom, or volume. Its QMK/VIA support is also listed for configuring keys and knobs.
Neither product has a compatibility rule listed in its product details. The Retro18 vendor description names Windows and Android, while the KM21 Ultra vendor description lists Windows, macOS, Linux, Android, and iOS via Bluetooth.
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