Official specs from Steam

Tomb Raider: Underworld system requirements

Minimum and recommended PC specs as listed by the developer on Steam.

Minimum

Supported OSMicrosoft Windows XP (admin rights required)/Microsoft Windows Vista (admin rights required)
ProcessorIntel Pentium 4 3+GHz or AMD Athlon 2.5+GHz
Memory1GB (Windows XP) / 2GB (Windows Vista) system memory
Graphics CardNVIDIA GeForce 6 series 6800GT (or better) / ATI 1800XT (or better)
Sound CardDirect X 9.0c compatible sound card and drivers
Hard Drive Space8 GB Free Space

Recommended

Supported OSMicrosoft Windows XP (admin rights required)/Microsoft Windows Vista (admin rights required)
ProcessorIntel Core 2 Duo 2.2 GHz or Athlon 64 X2 4400+
Memory2 GB system memory
Graphics CardNVIDIA GeForce 9800 GTX or ATI HD4800
Sound CardDirect X 9.0c compatible sound card and drivers
Hard Drive Space8 GB Free Space
ControllerMicrosoft Xbox360 Controller

FAQ

What graphics card do I need for Tomb Raider: Underworld?

Minimum: NVIDIA GeForce 6 series 6800GT (or better) / ATI 1800XT (or better). Recommended: NVIDIA GeForce 9800 GTX or ATI HD4800.

How much RAM does Tomb Raider: Underworld need?

Tomb Raider: Underworld needs 1GB (Windows XP) / 2GB (Windows Vista) system memory at minimum, 2 GB system memory recommended.

How big is Tomb Raider: Underworld?

Tomb Raider: Underworld requires 8 GB Free Space.

Does Tomb Raider: Underworld run on Mac or Steam Deck/Linux?

There is no native macOS version. There is no native Linux build (Proton compatibility may vary).