Regular brisk walking is a moderate-intensity aerobic workout that can tone and tighten legs. To become fit and burn fat overall -- including in your legs -- follow the guidelines of the Centers for Disease Control and Prevention and aim for 150 minutes of moderate-intensity walking per week along with two weekly strength-training workouts. How long it takes you to become toned after you begin your walking program depends on several factors, including the amount of body fat you currently have and how often you work out.
Calculate how much weight you have to lose by finding your body mass index. Weigh yourself on a reliable scale and measure your height. Multiply your height, in inches, by itself. Divide your weight by your squared height and multiply this result by 703. A 168-pound woman at a height of 65 inches, for example, has a BMI of 28.12, which the CDC considers to be overweight. In this case, you would have to stick to a strict walking regime to get toned, slim legs. Aim for a net reduction of 3,500 calories in combined diet and exercise every two weeks to achieve steady progress.
Monitor your intensity. Walk at a brisk pace, sufficient to get your breathing elevated, but not too intense that you cannot hold a conversation. A 168-pound woman, for example, who walks at a rate of 2 mph for 60 minutes, burns 211 calories, according to the website Health Status. The same woman walking at a rate of 4 mph will burn almost twice as many calories, at an average burn of 393 calories per hour.
Increase your resistance by walking up stairs. A 168-pound woman can supercharge her workout burning about 300 calories by walking up stairs for 30 minutes. Use the stairs at work or home -- or any available stairway -- to sneak in 10-minute walking breaks three times a day.
Combine your walking routine with a sensible diet to create leaner, more toned legs. Choose leafy green vegetables, fresh fruits, lean meats, whole grains and polyunsaturated fats, according to the U.S. Department of Agriculture 2010 dietary standards. Make small changes, such as eating smaller portions and filling up on fiber-rich foods to cut calories.