You’ve probably heard the standard recommendations to get 150 minutes of aerobic exercise per week at moderate intensity…or 75 minutes at vigorous intensity. But what does “moderate” really mean? And how much harder is “vigorous”?

If walking is your thing—and it is one of the best possible forms of aerobic exercise—there are lots of electronic fitness trackers (not to mention good, old-fashioned pocket pedometers) that promise to give you the answers. The problem is, these devices are not always affordable or convenient to use. And some people don’t like being “plugged in” all the time.

Now an ongoing study focusing on the health benefits of walking, which earlier research has pegged as everything from improved heart health to reduced risk for constipation, has uncovered an easy way to determine the intensity of your exercise—without using a pricey electronic device or a fancy pedometer.

New finding: In analyzing the first batch of results from their study-in-progress, researchers at the University of Massachusetts Amherst report that simply counting the number of steps you take per minute will determine your walking cadence—which is a surprisingly simple but reliable way to ensure that you’re exercising hard enough.

Study details: In this initial report, published in International Journal of Behavioral Nutrition and Physical Activity, 80 study participants (all from the 21- to 40-year-old group) were asked to walk on a treadmill for five-minute intervals with two-minute periods of recovery between each session. The treadmill speed was bumped up by half a mile per hour for each five-minute effort until the participant was running…working at 75% of his/her maximum heart rate…or self-reported as exercising at a “somewhat hard” level.

The researchers counted the walkers’ cadence, and their exercise intensity was verified by a portable device that calculates oxygen consumption. With these results in hand, the researchers found that walking cadence is a good indicator of exercise intensity.

The numbers you need to know: A walking speed of moderate intensity begins at approximately 100 steps per minute, according to this study, while a vigorous intensity kicks in at about 130 steps per minute.

To quickly calculate your own cadence on any given walk: Wear a watch with a second hand (or set the timer on your smartwatch) and go for a walk. Simply count the number of steps you take in 15 seconds, then multiply that number by four. Voila! That final number is your walking cadence.

To put a little groove into your step: If you hum “Stayin’ Alive” by the Bee Gees to yourself while you walk, and match your steps to the beat, you’ll be right at 100 steps per minute. Walking to the beat of Cyndi Lauper’s “Girls Just Wanna Have Fun” or Billy Ray Cyrus’s “Achy Breaky Heart” will put you at a cadence of 120. And to boost your effort up to 130, step out to Jennifer Lopez’s “On the Floor” or Lady Gaga’s “The Edge of Glory.”