Health & Fitness
Health and fitness calculators built on NHS, EFSA, ADA and peer-reviewed figures: BMI, body fat, FFMI, A1C, water intake, steps, due date and 1RM.
Health and fitness calculators turn your measurements into the figures that doctors, coaches and public health bodies use, and each one names the source behind its numbers. They cover weight, body composition, blood sugar, hydration, walking, pregnancy and strength training, in metric or imperial units.
The BMI Calculator uses the NHS adult ranges, where 18.5 to 24.9 is a healthy weight, and applies the lower thresholds the NHS sets for people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds. It is for adults aged 18 and over. The Body Fat Calculator uses the US Navy tape-measure equations from your neck, waist and, for women, hip measurements, and the FFMI Calculator turns a body fat figure into lean mass and fat-free mass index.
The A1C Calculator converts HbA1c between % and mmol/mol and estimates average blood glucose with the ADAG formula, so an A1C of 7% is 53 mmol/mol and about 154 mg/dL. UK and US thresholds differ: Diabetes UK puts diabetes at 48 mmol/mol or above, while the CDC and ADA use 6.5% or above. The Water Intake Calculator uses EFSA's adequate intakes of 2.0 litres of total water a day for women and 2.5 litres for men, or the US National Academies' 2.7 and 3.7 litres, from food and drink together.
The Steps to Miles Calculator converts a step count using your measured step length or the common estimate of 2,000 steps a mile, with optional calories. The Due Date Calculator adds 280 days to the first day of your last period, adjusts for cycle length as the NHS calculator does, and also works from a conception or IVF transfer date. The One Rep Max Calculator estimates your 1RM with the Epley and Brzycki formulas: 100 kg lifted 5 times gives about 114.6 kg on average.
Every result is an estimate for healthy adults and a starting point for a conversation with your GP, doctor, midwife or coach, not a diagnosis.
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BMI Calculator
Work out your adult BMI in metric or imperial, see which NHS category it falls in and the healthy weight range for your height.
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Due Date Calculator
Estimate your baby's due date from your last period, conception date or IVF transfer, and see how many weeks pregnant you are today.
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One Rep Max Calculator
Estimate your one-rep max (1RM) from any weight and reps using the Epley and Brzycki formulas, in kg or lb, with a percentage table.
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Water Intake Calculator
Work out how much water to drink a day from EFSA and US National Academies reference intakes, in litres, ml, fl oz and glasses.
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Steps to Miles Calculator
Convert steps to miles and kilometres using your measured step length or the common 2,000 steps a mile estimate, with optional calories.
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A1C Calculator
Convert HbA1c between % and mmol/mol, turn A1C into estimated average blood sugar in mg/dL or mmol/L, and see UK and US ranges.
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FFMI Calculator
Work out your fat-free mass index (FFMI), normalised FFMI, lean mass and fat mass from your height, weight and body fat percentage.
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Body Fat Calculator
Estimate your body fat percentage with the US Navy tape method from your height, neck, waist and (for women) hip measurements, plus fat mass.
Common questions about health & fitness
How much water should I drink a day?
EFSA sets an adequate intake of 2.0 litres of total water a day for women and 2.5 litres for men, from food and drink together, and about 70 to 80% of that usually comes from drinks. The US National Academies use 2.7 and 3.7 litres. You need more in hot weather or when you exercise.
How many steps are in a mile?
About 2,000 for an average adult walking, which is the common estimate, but it depends on your step length. With a step of 76.2 cm, 10,000 steps is 7.62 km or 4.73 miles. The Steps to Miles Calculator uses your own step length if you measure it over 10 normal steps.
What is a healthy BMI for adults?
For adults the NHS treats 18.5 to 24.9 as a healthy weight, 25 to 29.9 as overweight and 30 or more as obese. Lower thresholds apply to some ethnic groups, where 23 counts as overweight. BMI does not measure body fat directly, so treat it as a starting point rather than a diagnosis.
What average blood sugar does an A1C of 7% mean?
About 154 mg/dL, or 8.6 mmol/L, using the ADAG study formula (28.7 × A1C − 46.7). 7% is 53 mmol/mol, which is in the diabetes range in both the UK (48 or above) and the US (6.5% or above). Only your own tests and your doctor can diagnose diabetes.
How is my due date calculated?
Your due date is 280 days, or 40 weeks, after the first day of your last period. If your last period started on 10 January 2026, your estimated due date is 17 October 2026. This assumes a 28-day cycle, and the dating scan at 10 to 14 weeks may move the date.