Sleep and Fitness Tools from the Duplex

Three sleep and fitness tools, one rule: show the math

Step count: there are three calculators here right now. Each one does one job, shows its result in plain numbers and then shows its work. That last part is the rule. If a calculator uses a number you didn't type in, the number is listed under the result with a link to where it came from.

That's how I'd want a support ticket answered, too. Here's the fix, here's why it works, here's the documentation. (Margo says I talk about everything like a support ticket. Margo is not wrong.)

• Sleep calculator — when to go to bed for a wake-up time, when to wake up for a bedtime, and when to end a nap. Written up by Rosa, who has an alarm at 4:10 a.m. and opinions about it.
• How many steps in a mile — steps to miles and kilometers, and back, at your walking pace or with your own measured step. Mine.
• Bedding size guide — standard mattress sizes, the fitted-sheet pocket depth you need, and the smallest comforter, duvet, blanket or throw that covers your bed. Margo's, and she measured twice.

How the sleep calculator works

The sleep calculator counts your night in sleep cycles. According to the NHLBI, part of the National Institutes of Health, a sleep cycle starts over every 80 to 100 minutes, and there are usually four to six cycles a night. The calculator uses 90 minutes, the middle of that range.

It also adds the time it takes to fall asleep. The default is 15 minutes, and you can change it. That default isn't random: CDC guidance for nurses on fatigue suggests relaxation techniques if falling asleep takes longer than 15 to 25 minutes, and another NIOSH training page puts normal sleep onset at up to about 25 minutes.

Pick your age, and each bedtime gets checked against the CDC's recommended hours: 7 or more for adults 18 to 60, 7 to 9 for 61 to 64, 7 to 8 for 65 and older, 8 to 10 for teens and 9 to 12 for kids 6 to 12. Rows that fit the range are marked.

The nap mode follows NIOSH's advice for nurses: a short nap with an alarm 15 to 30 minutes after you lie down, or one full cycle of about 90 minutes plus the time to fall asleep. Waking in the middle, around an hour in, is the groggy option.

What it can't do: tell you why you're tired, or promise you'll feel rested. It's a planning tool, the same way a calendar is. If sleep problems keep up, the right next step is a conversation with your doctor, not a better calculator.

How the steps-to-miles calculator works

The number of steps in a mile depends on how long your steps are, and step length changes with pace. Faster walkers take longer steps, so a mile takes fewer of them.

Instead of guessing from your height, the calculator uses measured data. A 2011 review by Tudor-Locke and colleagues in the International Journal of Behavioral Nutrition and Physical Activity collected treadmill studies that counted steps per minute at set speeds. From one of those studies:

Speed	Steps per minute	Steps in a mile
2.4 mph	109	about 2,725
3.0 mph	115	about 2,300
3.5 mph	124	about 2,126
4.1 mph	134	about 1,961

Steps in a mile is steps per minute times 60, divided by the speed in mph. At 3 mph that's 115 × 60 ÷ 3 = 2,300. Pick a pace and the calculator uses that row.

If you'd rather use your own step, measure it. Walk 10 normal steps, measure the distance from where you started to where you stopped, and divide by 10. Then a mile is 63,360 inches divided by your step length. Unit conversions come from NIST, so a mile is 1.609344 kilometers and an inch is 2.54 centimeters, exactly.

The same review is where the "how many steps a day" question gets a real answer instead of a slogan. It reports that healthy adults typically take between 4,000 and 18,000 steps a day, and calls 10,000 steps a day reasonable for that group. The CDC's guideline for adults is written in minutes, not steps: 150 minutes a week of moderate activity, such as brisk walking, plus muscle-strengthening on at least 2 days.

I made a spreadsheet of my step counts by pace. Margo asked if I was okay. I said yes, at 3 mph.

The result is an estimate. Your phone counts steps one way, your watch another, and a treadmill measures distance from its belt. They'll all disagree a little, and that's normal. Check with your doctor before starting a new exercise routine.

How the bedding size guide works

The bedding guide is the most literal tool of the three. It doesn't estimate anything. It adds and subtracts.

Standard US mattress sizes come from the Better Sleep Council, an education group backed by the International Sleep Products Association: Twin 38 × 75 inches, Twin XL 38 × 80, Full 53 × 75, Queen 60 × 80, King 76 × 80 and California King 72 × 84. If your tape measure says something different, use your numbers. The calculator takes custom sizes.

From there:

1. Fitted sheet. The pocket depth needs to be at least as deep as your mattress, topper included.
2. Anything that lies on top. A flat sheet, comforter, duvet, blanket or throw needs the mattress width plus twice the overhang you want, and the mattress length plus one overhang at the foot.
3. Label check. Type in the finished size from a label, and the calculator shows how far it hangs over each side and the foot of your mattress.

US labeling rules help here. Under the uniform labeling regulation published by NIST, fitted sheets state the size of the mattress they're made for, flat sheets state both the mattress size and the finished size, and blankets and comforters state their finished size. The numbers you need are already on the package. The guide tells you which ones to compare.

What it doesn't do: copy any maker's size chart. Makers' charts are on their own sites, and they differ, which is the whole reason to check the label of the one you're looking at.

Why the tools don't ask for anything else

No accounts, no email, no saving. I've closed enough support tickets about lost passwords to know that a calculator doesn't need one. The tools work with what you type, show you the answer and forget it when you close the tab.

There's also nothing to sell inside the calculators themselves. Where a tool fits a kind of product, like the bedding guide and sheets or comforters, a short list of products may appear under it once listings are checked, with a Check price button that goes to Amazon. That's how the site earns, and the disclosure page explains it. The calculator's answer never depends on it.

Using the three together

Here's a winter evening in the duplex, run through the tools:

• Rosa needs to be up at 4:10. The sleep calculator says five cycles plus 15 minutes to fall asleep means in bed by 8:25 p.m. She has opinions about that, and Margo has opinions about her opinions.
• I walked laps of the upstairs hallway between calls and my phone says about 4,600 steps. At a 3 mph pace that's about 2 miles. (Margo would like those laps to happen with slippers on.)
• Margo is checking a comforter for the guest room. Queen mattress, 12 inches deep, and she wants it to hang to the bottom of the mattress. The guide says the comforter needs to be at least 84 × 92 inches. She reads the label next. Then the care tag. Then, eventually, the rest of the listing.

None of that took more than a minute. That's the goal. Keep walking.