The spread of residential broadband Internet access is raising the question of how to measure Internet speed. We argue that available bandwidth is a key metric of access link speed. Unfortunately, the performance of available bandwidth estimation tools has rarely been tested from hosts connected to residential networks. This paper compares the accuracy and overhead of state-of-the-art available bandwidth estimation tools from hosts connected to commercial ADSL and cable networks. Our results show that, when using default settings, some tools underestimate the available bandwidth by more than 60%. We demonstrate using controlled testbeds that this happens because current home gateways have a limited packet forwarding rate.