What affects a material's resistance

If you are using a wire made out of (say) iron the formula would be

R = k * L / (pi * r^2)

pi r^2 represents the cross sectional area.

L is the length of the wire.

k is the resistance constant for that material.

So, resistance is measured as

k which depends on the material. It is different for all materials. Copper Silver and Gold for example, all have different k values.

L is the length of the material

pi * r^2 is the area of a thin slice of this material.