How long should it take to get up to strength after not lifting for a month?

How Do You Define Strength?. This is a loaded question, based on what you define as 'strength'. If it means a specific amount of 'weight' you could previously lift, then 3-4 weeks of a sound, safe, progressive, well-balanced, strength training program should get you well on your road. Take a month off, if other exercise was completed, isn't that big a deal. Six months to a year, on the other hand would require a much more conservative progression. Keep a few thing in mind as you gear up your strength program: 1) For pure strength gains, work at about 85% of your max for 6-8 reps per exercise. That means the weight is high, the reps are low. Working with too light a weight for high reps will not produce the strength gains it sounds you are looking for 2)Work large muscle groups first - this will allow you to use your energy efficiently before tiring out working smaller muscles groups first (i.e. back before biceps) 3) Your lifting speed should be slow and controlled. This will promote more blood flow to the working muscles, hence increasing muscle hypertrophy and strength.