The gauge number of a mattress coil indicates the mattress’ firmness. The lower the gauge number of the mattress coil, the thicker the coil. Therefore, the lower the gauge number, the firmer and stiffer the mattress will feel, offering a harder surface for the mattress.Mattresses with lower coil gauges typically last longer because the thicker wire wears out slower over time. However, most consumers replace their mattress before the coils wear out, regardless of their gauge, and therefore gauge number should not be a heavy consideration in regards to durability.