Redstone circuits/Logic/OR

Minimal OR Gate (A)

1×1×2 (2 block volume)
flat, silent, instant
circuit delay: 0 ticks

Minimal OR Gate

Torch-isolated OR Gate (B)

1×3×2 (6 block volume)
silent, flat, isolated-input
circuit delay: 2 ticks

Torch-isolated OR Gate

Repeater-isolated OR Gate (C)

2×n×3 (12+ block volume)
flat, silent, isolated-input
circuit delay: 1 tick

By staggering heights, n inputs can be added. Note that a block is above the darkened input.

Repeater-isolated OR Gate

Vertical OR Gate (D)

1×4×4 (16 block volume)
1-wide, silent, isolated-input
circuit delay: 2 ticks

Slab-isolated OR Gate (E)

3×n×3 (12+ block volume)
silent, isolated-input, instant
circuit delay: 0 ticks

The design can be expanded to fit n inputs by increasing the length.

Design comparison

Design	Volume	Inputs	Isolated?	Redstone	Torches	Repeaters
A	2	3	No	1	0	0
B	6	3	Yes	1	1	0
C	6×n	n (Max 60)	Yes	n	0	n
D	16	2	Yes	4	2	1
E	9×n	n (Max ~30)	Yes	n×2	0	0