Subjective, but grading based on:
1: murmur is only audible on listening carefully for some time.
2: murmur faint but audible on placing the stethoscope on the chest.
3: loud murmur readily audible but with no palpable thrill.
4: loud murmur with a palpable thrill.
5: loud murmur with a palpable thrill. Audible with stethoscope rum just on chest
6. Audible with stethoscope off chest wall!