We have measured the total energy spread (99 persent energy spread) of the Booster beam at its injection energy of 400 MeV by three different methods - 1) creating a notch of about 40 nsec wide in the beam immediately after multiple turn injection and measuring the slippage time required for high and low momentum particles for a grazing touch in line-charge distribution, 2) injecting partial turn beam and letting it to debunch, and 3) comparing the beam profile monitor data with predictions from MAD simulations for the 400 MeV injection beam line. The measurements are repeated under varieties of conditions of RF systems in the ring and in the beam transfer line.