One of the smallest Intel mini PC we've seen so far was ECS LIVA Q2 Micro PC which Ian reviewed last year with an Intel Celeron N4000 Gemini Lake processor, 4GB RAM, and 32GB eMMC flash housed into a 70 x 70 x 33.4 mm (163.66 cm3) enclosure.
CHUWI LarkBox is a similar mini PC with an Intel Celeron N4100 SoC, 6GB RAM, 128GB, and various ports into a 61 x 61 x 43 mm enclosure, that's a bit taller but marginally smaller with a volume of 160 cm3.
Click to Enlarge
CHUWI LarkBox (preliminary)