Enlarge Reduce

Spell Lists. Artificer, Bard, Druid, Sorcerer, Wizard
2nd-level transmutation
Casting Time: 1 action
Range: 30 feet
Components: V, S, M (a pinch of powdered iron)
Duration: Concentration, up to 1 minute

You cause a creature or an object you can see within range to grow larger or smaller for the duration. Choose either a creature or an object that is neither worn nor carried. If the target is unwilling, it can make a Constitution saving throw. On a success, the spell has no effect.

If the target is a creature, everything it is wearing and carrying changes size with it. Any item dropped by an affected creature returns to normal size at once.

Enlarge. The target’s size doubles in all dimensions, and its weight is multiplied by eight. This growth increases its size by one category – from Medium to Large, for example. If there isn’t enough room for the target to double its size, the creature or object attains the maximum possible size in the space available. Until the spell ends, the target also has advantage on Strength checks and Strength saving throws. The target’s weapons also grow to match its new size. While these weapons are enlarged, see below for weapon Size shift Effects

Reduce. The target’s size is halved in all dimensions, and its weight is reduced to one-eighth of normal. This reduction decreases its size by one category – from Medium to Small, for example. Until the spell ends, the target also has disadvantage on Strength checks and Strength saving throws. The target’s weapons also shrink to match its new size. While these weapons are reduced, see below for weapon Size shift Effects

Weapon Size Shift:
The dice of the base weapon is shifted when enlarge/reduced based on damage dice, the short answer is to "shift by 4" to the weapon dice rolled, but that wont always work the best. Here is a table

Reduced	Normal	Enlarges
1	1d4	1d8
1	1d6	1d10
1d4	1d8	1d12
1d6	1d10	3d4
1d8	1d12	2d8

Eg. GreatSword: L 2d6 --> H (d6 => d10) 2d10 --> G 6d4 -- C 6d8
Glaive: L 1d10 --> H (d10 => 3d4) 3d4, --> G (d4 => d8) 3d8 --> C 3d12
Dagger: S d4 --> M d8 --> L 1d12 --> H 2d8 --> G 2d12 --> C 4d8