Let N ≥ 2 and let 1 < a 1 < · · · < a N be relatively prime integers. The Frobenius number of this N -tuple is defined to be the largest positive integer that cannot be expressed as N i=1 a i x i where x 1 , . . . , x N are non-negative integers. The condition that gcd(a 1 , . . . , a N ) = 1 implies that such a number exists. The general problem of determining the Frobenius number given N and a 1 , . . . , a N is NP-hard, but there have been a number of different bounds on the Frobenius number produced by various authors. We use techniques from the geometry of numbers to produce a new bound, relating the Frobenius number to the covering radius of the null-lattice of this N -tuple. Our bound is particularly interesting in the case when this lattice has equal successive minima, which, as we prove, happens infinitely often.