Caffeine Calculator
How much caffeine your drinks add up to in a day, using USDA FoodData Central values, against the 400 mg FDA figure or a lower limit, and how much is left in your body hours later.
Result…
How it's calculated
Caffeine (mg) = volume (mL) × caffeine per 100 g ÷ 100 × grams per fl oz ÷ 29.5735295625 1 US fl oz = 29.5735295625 mL Share of limit = total ÷ limit × 100 Left after t hours = total × 0.5^(t ÷ half-life)
Each drink uses its USDA FoodData Central SR Legacy entry (FDC IDs shown under each field): the caffeine in mg per 100 g, turned into mg per mL with the same entry's gram weight for one fluid ounce. Totals are compared with the FDA's figure of 400 mg a day for most adults, the NHS limit of 200 mg a day in pregnancy, or a limit you enter. The time curve is a simple half-life model that treats the day's caffeine as taken at once; EFSA's caffeine opinion gives a half-life of about 4 hours in adults (range about 2 to 8), longer in pregnancy, so the visitor can change it.
Your numbers, step by step
About the Caffeine calculator
Coffee, tea, cola and energy drinks all add caffeine, and the amounts are easy to lose track of. This calculator adds up a day's drinks from the amounts you enter in millilitres or US fluid ounces. It uses caffeine values from USDA FoodData Central, and each field names its FoodData Central entry. A separate field takes caffeine in mg from product labels. The total is compared with the FDA's figure of 400 mg a day for most healthy adults, the NHS limit of 200 mg a day in pregnancy, or a limit you enter. A half-life model then shows how much caffeine is still in your body hours later, which helps when you are thinking about sleep. The default half-life is 4 hours, as given by the European Food Safety Authority, and you can change it.
How to use it
- Choose “mL” or “US fl oz” under “Amounts in”.
- Enter how much of each drink you had today, and any caffeine from labels under “Other caffeine from labels”.
- Pick the limit under “Compare with”, or choose “A limit I enter”.
- Set the “Caffeine half-life” and the “Hours after drinking it” to see what is left later.
Worked example
480 mL (about 16 fl oz) of brewed coffee and 240 mL (about 8 fl oz) of black tea. Coffee: 40 mg per 100 g × 29.6 g per fl oz ÷ 29.5735 mL = 0.4004 mg/mL, so 480 mL gives 192.2 mg. Tea: 0.2002 mg/mL, so 240 mL gives 48.0 mg. The total is about 240 mg, which is 60% of 400 mg. With a 4-hour half-life, about 60 mg is left after 8 hours.
Updated
Questions people ask
How do I work out how much caffeine I have had today?
Multiply each drink's volume by its caffeine per mL and add the results. The calculator takes the per-mL values from USDA FoodData Central entries. For products with a label, enter the label's mg directly.
How much caffeine is too much in a day?
The FDA cites 400 mg a day as an amount not generally linked with negative effects for most adults. The NHS advises no more than 200 mg a day in pregnancy. Advice differs by country, and people differ in how sensitive they are.
How long does caffeine stay in your body?
EFSA gives a half-life of about 4 hours in adults, with a range of about 2 to 8 hours. After one half-life, half is left; after two, a quarter. It takes longer in pregnancy.
Why does my coffee shop drink have more caffeine than this shows?
Caffeine varies with the bean, the roast, the brew strength and the cup size. The FDC values are averages. Ask the seller, or use the label figure in the “Other caffeine from labels” field. Brew strength is covered in the coffee ratio calculator.
Is decaf coffee caffeine-free?
No. The FDA notes that decaf usually has 2 to 15 mg in an 8 fl oz cup. The FDC entry used here gives 1 mg per 100 g.
Can I rely on this if I am pregnant or take medicines?
Use it only as a rough guide. Pregnancy, some medicines and some health conditions change how fast caffeine clears and how much is safe. Ask your doctor, midwife or pharmacist for your own limit. The adult figure is from the FDA.