Why the Scale Is a Poor Measure of Progress

Quick Intro

The scale measures everything in your body at once: muscle, fat, bone, water, stored carbohydrate and the food in your gut. Several of those change from day to day for reasons that have nothing to do with fitness or fat. A scale also cannot tell you whether you have lost fat and gained muscle at the same time. That makes it a poor guide to whether training is working.

This article explains why weight moves around, how to weigh yourself usefully if you choose to and what shows progress better.

Why Weight Moves Around

Body weight commonly shifts by up to a kilogram or so between days, and sometimes more, without any change in fat. The main reasons:

Water. Your body holds more or less water depending on salt, heat, hormones, stress and sleep.
Stored carbohydrate. Muscles store carbohydrate as glycogen, and each gram of it is stored with several grams of water. A day of more carbohydrate, or a new training routine, can raise weight a little. A low-carbohydrate day or a long, hard session can lower it.
Food and drink. What is in your stomach and gut at the time you step on the scale adds weight until it is digested and passed.
Weekly patterns. In a study of adults who weighed themselves regularly, weight tended to rise over weekends and fall during the week, and it peaked around holidays.

These shifts can easily hide or exaggerate real changes in fat over a week or two.

The Scale Cannot See Muscle and Fat

When you start strength training, you may gain some muscle while losing some fat, a process called body recomposition. The scale might stay the same, or even rise, while your body becomes leaner and stronger.

Regular aerobic exercise can also reduce your waist and the fat stored around the organs, the fat most linked to health risk, while body weight hardly moves. Someone looking only at the scale would see no change at all.

If You Want to Weigh Yourself

Weighing can still be useful as one measure among several, if it does not upset you. To make it more meaningful:

Weigh at the same time and in the same conditions, such as first thing in the morning after using the toilet and before eating.
Compare the same day each week, or use a weekly average, to smooth out daily swings and weekend patterns.
Look at the trend over several weeks, not single readings.
Expect noise. A rise of half a kilogram after a salty meal or a hard session is water, not failure.

If weighing yourself makes you anxious or drives you to extreme choices, it is fine to stop and use other measures instead.

Better Measures of Progress

These tell you more about fitness and body composition:

Waist measurement. Measured every few weeks at the same point, around the navel, it reflects changes in fat around the middle better than weight.
How clothes fit. Simple and surprisingly informative.
What you can do. More repetitions, heavier weights, longer holds, faster or longer walks.
How daily tasks feel. Easier stairs, carrying shopping and getting up from the floor.
The talk test. Talking more easily at the same walking pace shows stamina improving.
Resting heart rate. A slow downward drift over months reflects better aerobic fitness.
Photos. Taken in the same light and position every month or two, if you find them helpful.

How to tell you are getting fitter explains several of these in more detail.

How to Measure Your Waist

A waist measurement takes a minute and needs only a soft tape measure.

Stand up straight with your feet together and your stomach relaxed. Do not pull it in.
Wrap the tape around your middle at the level of your navel. Keep it level all the way round, snug without pressing into the skin.
Breathe out normally and read the number at the end of the breath.
Write it down with the date.

Measure at the same point and the same time of day every three or four weeks. A difference of a centimetre or so can come from how the tape sits, so look for a change that holds across two or three measurements.

Who This Applies To

This applies to most people training for health and fitness. If a doctor is monitoring your weight for a medical reason, follow their advice on when and how to weigh yourself.

FAQ

Why did I gain weight after a hard workout?

Hard sessions can cause muscles to hold extra water while they recover. This passes within a few days.

How often should I weigh myself?

If you weigh yourself, once a week at the same time is enough, or daily with a weekly average. Many people do well without weighing at all.

My weight has not changed but my clothes are looser. What is happening?

You have probably lost some fat and gained some muscle. That is good progress the scale cannot show.

Are smart scales that measure body fat accurate?

They give rough estimates that change with hydration. Use them for trends if you like, not exact numbers.