Baby Size Fruit and Vegetable Calculator

What this calculator does

Find out which fruit or vegetable weighs about the same as a typical baby at your week of pregnancy. Pick your week, or enter your last period or due date. You get the closest match, how the two weights compare, and a chart for every week from 10 to 40.

The baby's weight is a typical average for the week, not a measurement of your baby. Babies vary a lot, and only an ultrasound by your healthcare provider measures your own baby. The produce weights come from the U.S. Department of Agriculture (USDA), so each comparison is a real, checkable number.

Where it's used

Why this math matters outside the classroom:

• Comparing weights. Students divide 331 g by 336 g to get 0.99 and see that a typical 20-week baby and a mango weigh about the same.
• Produce shopping. Shoppers estimate a bag of 6 medium bananas at about 6 × 118 g, which is 708 g, before it reaches the scale.
• Grams to ounces. A 552 g cantaloupe is about 19.5 oz after dividing by 28.35, a little more than one pound.
• Weekly growth. Families track a typical baby growing from 35 g at week 10 to 3,619 g at week 40, about 100 times heavier.

How to use it

1. Choose how to start: the week you're in, the first day of your last period, or your due date.
2. Enter the week (10 to 40) or the date. For the date options, "Counting from" starts as today; change it to check another day.
3. Read the closest fruit or vegetable. Below it is the ratio, the typical weight and the typical length.
4. Open the table to see the matching produce for every week.

What the inputs mean

Week of pregnancy

Completed weeks since the first day of your last period. For example, 20 weeks 4 days counts as week 20.

First day of last period

The first day of bleeding of your most recent period. The calculator assumes a 28-day cycle.

Estimated due date

The date your healthcare provider gave you, or one from a due date calculator.

Counting from

The day to work out the week for. It starts as today.

Formula and method

Typical weight (g) = e^(0.578 + 0.332 × W − 0.00354 × W²)
Ratio = typical weight ÷ produce weight
Closest item = the one whose ratio is nearest to 1
Fair match when the ratio is between 0.67 and 1.5

W is the number of completed weeks of pregnancy. The letter e is a fixed number, about 2.718. The weight formula comes from Hadlock and colleagues (1991). It gives the middle weight for each week: half of babies weigh more and half weigh less.

The ratio tells you how the two weights compare. A ratio of 1 means the same weight. A ratio of 1.2 means the baby is 20% heavier, and 0.8 means it is 20% lighter.

The calculator picks the item with the ratio nearest to 1. It judges "nearest" by proportion, so being 10 g off a 50-g fig counts the same as 100 g off a 500-g melon. If even the nearest item were more than 1.5 times heavier or lighter, the page would say there's no close match.

Worked example

You are 20 weeks pregnant. Which fruit or vegetable weighs about the same as a typical baby?

1. Weight formula: 0.578 + 0.332 × 20 − 0.00354 × 20² = 5.802.
2. Undo the log: e^5.802 = 331 g, about 11.7 oz.
3. The nearest produce item is a mango at 336 g. Ratio: 331 ÷ 336 = 0.99.
4. 0.99 is between 0.67 and 1.5, so the mango is a fair match.

Result: At 20 weeks, a typical baby weighs about 331 g (11.7 oz), about the weight of a mango.

Understanding the result

Weight and size are not the same thing. A typical baby at 20 weeks weighs about as much as a mango, but the two have very different shapes. Two things can weigh the same and still take up very different amounts of space.

A fruit weight is also an average, and real produce varies. The USDA lists a small peach at 130 g and an extra-large one at 224 g. Variety, ripeness, growing weather and even how long it sat in the store all change the number. Fruit loses water as it sits, so it gets lighter over time.

Watch the jump at week 34, when the match moves from a casaba melon to a small watermelon. The baby's growth is smooth. The jump comes from the gap between the two melons in the list.

Assumptions and limitations

• Weights are USDA FoodData Central figures for one raw item of a stated size, such as "1 medium" or "1 melon". The USDA weighs the part you eat, so pits, peels and rinds are often left out.
• The week is counted from the first day of the last period, with a due date 280 days after that day. Sizes are given for whole weeks.
• From 41 weeks to 42 weeks 6 days, the 40-week figures are shown, since the weight formula stops at 40 weeks.
• These are averages, not a measurement or a prediction for any one baby. Twins and other multiples are often smaller.
• The match uses weight only. A fruit and a baby of the same weight can look very different in size and shape.
• No length is shown for weeks 14 to 23, because no reliable published average exists for those weeks.
• It is not a medical tool. It can't detect any problem, and it doesn't replace prenatal care.

Frequently asked questions

How this calculator is checked

Method: Typical weight: Hadlock, Harrist & Martinez-Poyer, Radiology 1991;181:129–33, 50th-percentile equation (10–40 weeks), with lengths and dating as in src/lib/health/fetal-size.ts. Produce weights: USDA FoodData Central portion weights (SR Legacy 2018 and Survey/FNDDS 2024 bulk downloads), each cited by food ID in items.ts. Matching: closest weight on a ratio scale, with a 1.5× limit for a fair match. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-26. Found a problem? Tell us.

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