How much electricity does a 220v 110v transformer use in stand by mode?

A transformer in standby mode typically consumes a small amount of electricity, known as "no-load loss" or "core loss," which is primarily due to the magnetization of the core. This loss is generally low, often ranging from 1 to 5 watts for smaller Transformers. The exact amount can vary based on the transformer's design and efficiency. Overall, while the power consumption is minimal, it can accumulate over time if the transformer remains in standby for extended periods.