· 3 min read
A Buffer Holds Its pH by a Ratio, So Dilution Changes Nothing
Equal amounts of a weak acid and its base give pH = pKa exactly, at any concentration. Blood runs the same equation at a 20:1 ratio and lands on 7.40.
Sofia Nunes
Health & wellness writer at OneKitly
Nutrition, hydration and healthy habits
Sofia writes approachable, evidence-based wellness content on nutrition, hydration and sustainable healthy habits. She always points readers to qualified professionals for personal medical advice.
Expertise
- Nutrition
- Hydration
- Body metrics
- Healthy habits
- Sleep
Track record
- Writing since 2018
- 92 guides published on OneKitly
- 89 of them on health
- 322 sources cited
- from 171 distinct publishers
- Publishing on OneKitly since August 21, 2025
How Sofia works
Sofia works from public-health guidance and the published reference intakes behind it — the health authority and its advisory body, not a secondary summary of either. Where the evidence is contested she says so, and every article states plainly that general guidance does not replace a professional who knows the reader's own case.
Articles by Sofia Nunes
Start here
Ranked by how many pages of this site link to them, not by traffic.
Subjects
Guides published under this byline in each section. Each link opens the section in full, across all writers.
Latest publications
· 3 min read
Osmotic Pressure Counts Particles, Not Molecules
0.15 M of a salt that splits in two and 0.30 M of one that does not give the identical 7.64 atmospheres. Only the particle count reaches the membrane.
· 3 min read
Four Hours a Day of Screen Is Sixty-One Days a Year
Four hours a day is 28 a week and 1,460 a year — 60.8 full days. Three hours is 45.6 days and seven is 106.5. The conversion is arithmetic; what it means is not.
· 3 min read
One Milligram per Litre Is One ppm — in Water, and Only There
50 mg in a litre is 50 ppm, because a litre of water weighs a million milligrams. Change the liquid, or move to air, and the two units stop agreeing.
· 3 min read
8.25 a Day Is 3,011 a Year, and Only One of Those Numbers Changes Anything
Fifteen cigarettes a day from packs of twenty at 11 costs 8.25 daily and 3,011.25 a year. The same amount saved instead, for twenty years at 5 %, comes to about 99,570.
· 4 min read
One Bust, Five Numbers — and Only the Collar Is a Measurement
A 34-inch bust is a US 6, a UK 10, a German 36, a French 38 and an Italian 42. Five labels, one body — while a men's shirt collar prints the neck measurement itself.
· 6 min read
Nappy Sizes Overlap, and the Smaller One Usually Wins
At 7.5 kg a baby is inside both the size 2 and the size 3 band. Take the 2: a snugger fit leaks less. The step to watch for is the weight at which the smaller band ends, and at 7.5 kg that is eight and a half months away.
· 6 min read
How Heart Disease Risk Scores Work — and Why They Disagree About You
Framingham, SCORE2 and the pooled cohort equations use overlapping but different inputs and were calibrated on different populations, so the same person gets three different percentages. Here is what each one asks for and what the number means.
· 6 min read
Biological Age vs Chronological Age: What Each One Actually Measures
Chronological age is exact. Biological age is not one thing but three — epigenetic clocks, blood-marker scores and lifestyle quizzes — and only the first two have published validation. Here is how to tell which one you are looking at.
· 6 min read
Waist-to-Hip Ratio Explained: The Thresholds, and Where to Put the Tape
WHO puts abdominal obesity at a ratio of 0.90 or more for men and 0.85 or more for women. But measuring in the wrong place changes the answer more than the threshold does — here is exactly where the tape goes.
· 6 min read
What Is a Normal Menstrual Cycle Length? The Numbers, by Life Stage
FIGO puts a normal cycle at 24 to 38 days; ACOG's older range is 21 to 35. Here is why two respected bodies give different numbers, how much variation is normal, and how cycles change after menarche and before menopause.
· 7 min read
How Blood Type Is Inherited: The Full Parent-to-Child Table
Each parent passes on one ABO allele — A, B or O — and Rh follows a separate gene. Here is every parent combination, which child types it can and cannot produce, and why this is not a paternity test.
· 6 min read
How Much Milk Does a Baby Need? The Rule of Thumb and Its Limits
A formula-fed baby takes roughly 2.3 fl oz per pound of body weight per day in the first months, split across the day's feeds. Here is the table by age and weight, why breastfed babies are not measured this way, and the signs that outrank any number.
· 4 min read
HbA1c to Average Blood Sugar: The Full Conversion Table
An HbA1c of 7 percent corresponds to an average glucose of about 154 mg/dL, or 8.5 mmol/L, or 53 mmol/mol. Here is the whole table, the formulas behind it, and when the number cannot be trusted.
· 5 min read
How to Calculate Keto Macros (Without Starting From the Percentages)
Set carbs as a fixed gram figure, protein by body weight, and let fat fill what is left. The famous 75 percent fat is an output of that calculation, not an input — and it drops on its own in a deficit.
· 4 min read
16/8, 5:2 or Alternate Day: The Fasting Protocols Compared
Five protocols side by side, what each demands, and the uncomfortable finding from the controlled trials: matched for calories, fasting loses about the same weight as simply eating less.
· 4 min read
How Much Weight to Gain in Pregnancy: The Guidelines by Starting BMI
The recommended range depends entirely on your BMI before pregnancy: 28 to 40 lb if you started underweight, 11 to 20 lb if you started with obesity. Here is the full table and the weekly rate behind it.
· 5 min read
How to Predict Your Next Period (And How Far Off the Estimate Can Be)
Add your average cycle length to the first day of your last period. Here is how to measure that length properly, why the estimate has a range rather than a date, and when irregularity is worth a consultation.
· 4 min read
Pregnancy Week by Week: The Calendar and What Each Stage Means
Pregnancy is counted in 40 weeks from your last period, not from conception — so you are already two weeks pregnant at conception. Here is the full calendar, the trimester boundaries and what term actually means.
· 2 min read
How Long Does Alcohol Stay in Your System?
The body clears roughly one standard drink per hour. See how long alcohol stays in blood, breath and urine — and why you can't rush it.
· 2 min read
How Much Water Should You Drink During Exercise?
Match your drinking to how much you sweat. Learn to estimate sweat rate and how much to sip per hour during a workout.
· 2 min read
Is BMI Reliable? The Limitations of Body Mass Index
BMI is a quick screen, not a diagnosis. Learn what it misses — muscle, fat distribution, age — and what to check alongside it.
· 2 min read
How Many Calories Are in a Pound of Fat?
A pound of body fat holds about 3,500 calories. See where the number comes from, why it's a rough guide, and how to use it for weight loss.
· 2 min read
What Is a Child Growth Percentile?
Growth percentiles compare a child's height and weight to others the same age and sex. Here's how to read them and what really matters.