There are three principles to keep in mind when taking body measurements:
Frequency: Repeat measurements with regular intervals that are short enough to provide timely feedback, but long enough that you can reasonably expect changes over repeated measures.
Reliability: Measurements should be taken in a repeatable manner, so that changes over time reflect true circumference changes, instead of just changes in measurement location or technique.
Relevance: Take measurements that are meaningful to you and your goals.
For most people, most of the time, we’d recommend taking measurements every week, every two weeks, or every month.
When you measure too frequently, it’s easy to focus on random day-to-day fluctuations instead of longer-term trends. You might find that measurements differ day-to-day by about a centimeter (¼-½ inch), but those day-to-day changes primarily reflect bloating, muscular swelling after exercise, and good old-fashioned measurement error. Sure, longer-term “true” changes will also be reflected in daily measurements, but you wind up with a worse signal:noise ratio. Measurements taken every week, every two weeks, or every month will still contain the signal – you’ll still be able to see measurements increase or decrease over time – but they remove most of the noise (random day-to-day fluctuations that aren’t indicative of longer-term changes).
Conversely, when you measure too infrequently, feedback isn’t sufficiently timely. Measurements should reflect outcomes that matter to you; you might measure changes in thigh or arm circumference as a proxy for muscle growth, waist circumference as a proxy for fat loss, or hip and shoulder circumference as a proxy for aesthetic goals. So, when you take a measurement, the measurement allows you to assess your progress toward your goals, and make adjustments to your plan if necessary. If you measure too infrequently (say, once every 3-6 months), you might end up identifying problems and making appropriate course corrections months after you should have.
Measuring weekly, every two weeks, or every month provides the ideal balance – you won’t get distracted or discouraged by day-to-day fluctuations, but you also won’t be flying blind without sufficiently timely feedback on your goal progress.
When measuring body circumferences, reliability is the primary concern. Reliability is roughly synonymous with consistency: If you measure the same circumference multiple times back-to-back-to-back, do you get the same result each time?
With reliable measurements, you can be confident that changes in your measurements reflect actual changes in body shape. With unreliable measurements, it’s harder to say if changes in your measurements reflect actual changes in body shape, or just measurement error and variability. So, here are some tips for taking reliable body measurements:
1) Take measurements under the same conditions each time.
The two primary considerations are intestinal contents and muscle swelling. For waist measurements, we’d recommend measuring first thing in the morning, before you’ve eaten. Intestinal contents can easily impact waist circumference measurements by an inch or two (2-5cm), so measuring your waist before you’ve eaten helps reduce variability.
For other circumference measurements, muscle swelling after an intense workout can affect circumference measurements up to half an inch (1-1.5cm). So, we’d generally recommend measuring circumferences when the muscles under the measuring tape aren’t noticeably sore. For example, if your biceps are sore, it may not be a bad idea to wait a day or two to measure your upper arm circumference. If your quads are sore, it may not be a bad idea to wait a day or two to measure your thigh circumference.
2) Be consistent about whether you flex your muscles, or leave them relaxed.
It’s totally fine to flex muscles that are under the measuring tape, and it’s also totally fine to keep your muscles relaxed. However, once you decide whether you want to measure limb circumferences with flexed or relaxed muscles, you should stick with that decision. Flexing your muscles can change limb circumference measurements substantially.
3) Make sure you measure at the same locations each time.
Circumference measures can change quite a bit based on the location of the measuring tape. So, for reliably tracking changes over time, it’s important to make sure you’re consistent about the location of your circumference measurements.
If you’re concerned that you may not remember the exact location of the tape measure for each of your circumference measurements, it can be helpful to jot down notes on a slip of paper you keep with your tape measure. Note the location of the tape measure, using whatever landmarks make the most sense to you. For example, you might note that you measure your waist circumference at navel-height, your flexed arm circumference at the largest point of your arm, your calf circumference at the point where the tape measure cuts through a birthmark, and your thigh circumference at the location of a perpetual tan line.
4) Practice and average.
Taking good, reliable circumference measurements is a skill. Just typing that sentence, I got flashbacks to grad school, where we had to take dozens (maybe hundreds) of consecutive limb and waist measurements on different people until our intra-rater reliability was high enough that we could be entrusted with live data collection.
Thankfully, it’s easier to measure your own limb circumferences than someone else’s, because you have more sensory feedback. If you squeeze the measuring tape a bit tighter around your leg, you’ll feel the difference in pressure, and if you situate the measuring tape a bit higher or lower around your hips, you’ll feel that it’s in a slightly different location. So, it shouldn’t take much practice to get reliable circumference measurements, but if you’ve never measured body circumferences before, it will probably take at least a little practice.
As a practical recommendation, I’d suggest practicing circumference measurements until 5 consecutive measurements fall within a 0.5cm range for smaller circumference measurements (arm, leg, and neck circumferences), and within a 1cm range for larger circumference measurements (shoulders, chest, waist, and hips).
Once you can take good, reliable measurements, I’d still recommend taking at least two measurements at each measurement site each time you assess body circumferences. If you get identical measurements back-to-back, you can confidently log that measurement. If you get slightly different measurements, take a third measurement, and average the two closest values.
For example, if you measure your waist at 86.5cm twice in a row, just record your waist circumference to be 86.5cm. However, if you measured your waist circumference to be 86.5cm on your first measurement, and 87cm on your second measurement, you should take a third measurement. If your third measurement is 86.3cm, average the two closest measurements (86.5cm and 86.3cm), and record their average (86.4cm) as your waist circumference.
5) Optionally, use a spring-loaded measuring tape.
Applying consistent pressure is key for taking reliable circumference measurements. By varying how tightly you squeeze the measuring tape, you can significantly alter a circumference measurement. It doesn’t take too long to learn how to apply the same level of pressure each time, but using a spring-loaded measuring tape can completely negate this concern, and help you take better, more reliable measurements with less practice required.
You have the option of recording up to 18 different circumference measurements in MacroFactor.
If you just like having more data for the sake of having more data, there’s certainly nothing wrong with tracking all 18 different body circumferences. However, I’d generally recommend focusing on a smaller selection of circumference measurements that actually matter to you. That way, recording body measurements will be less of a chore, and all of the data you collect will be meaningful and actionable.
Speaking personally, I only track my waist circumference and my right arm circumference (flexed, of course). I track my waist circumference because waist circumference is a pretty good predictor of heart disease risk (and waist-to-height ratio is even better), and I have a family history of heart disease. I track my flexed arm circumference because I’m also a meathead, and I want bigger arms. Beyond that, I don’t have a good reason to care about the other body circumferences I could measure. However, I’ll likely start taking other circumference measurements if they do become meaningful to me for some reason. For example, if I wanted to see how a new training program affected my calf growth, I’d start measuring my calf circumference when I started the new training program.
Your goals and priorities may be very different from mine. So, just make sure you’re selecting the measurements that are meaningful to you. If the measurements you take provide you with reliable, actionable insights about your progress toward a goal or outcome that matters to you, you’ll find it easier to consistently take high-quality measurements.