As of 13 August 2026, AI can only partly estimate your portion sizes.

What to actually do

1. Hand it to a person

   The route this page recommends

   A person who owns the outcome does this end to end, worth it when the failure is dear.

2. Use a tool built for this

   Second choice

3. Do it yourself

   The distant third

   A chat interface, chat-fluent skill, and roughly 30 minutes until you can act on the result.

   How to actually do it

   1. Open the NHS healthy eating guidance on NHS.uk so you have a general UK reference for balanced meals.
   2. Gather your usual meals, snacks, dietary pattern, allergies, activity level, goal and any relevant health conditions or medicines.
   3. Paste the prompt into ChatGPT, Claude or Gemini and replace each bracketed slot with your information, writing "none known" where it applies.
   4. Paste in the food labels, recipe quantities or photos converted into words for any specific foods whose portions you want estimated.
   5. Ask the model to revise any portion that is not given in a household measure you can use, such as a slice, spoonful, handful or mug.
   6. Compare the general guidance with the NHS information you opened, then use a GP or registered dietitian for personalised advice if you have a medical condition, pregnancy, medicine-related dietary need or a difficult relationship with food.

   Prompt

   Estimate practical food portion sizes for me using the information below. Give household measures, such as tablespoons, slices, handfuls or a mug, and grams only where they are useful. Separate general healthy-eating guidance from anything that would require a dietitian or clinician. Do not diagnose me, prescribe a diet, claim that the portions are medically right, or invent nutritional values. If my information suggests a medical condition, pregnancy, a history of an eating disorder, medicine-related dietary needs, unexplained weight change, or another higher-risk situation, do not personalise the portions and tell me to ask a GP or registered dietitian instead. If I mention urgent or worrying symptoms, tell me to contact NHS 111. Use the NHS Eatwell guidance as a general UK reference and state clearly where it does not answer my individual question. Show your assumptions, give a simple portion guide for each food group, then give one example for [breakfast], [lunch], [dinner] and [snack]. Ask up to three necessary follow-up questions before estimating anything.
   
   My information:
   - Age range: [age range]
   - Sex, if relevant to the estimate: [sex or prefer not to say]
   - Height and weight, if I know them: [height and weight or not known]
   - Usual activity: [mostly sitting, moderately active, very active, or description]
   - Goal: [maintain weight, gradual weight loss, gain weight, improve meal balance, or other]
   - Dietary pattern, allergies and foods avoided: [details]
   - Usual meals and snacks: [details]
   - Health conditions, medicines, pregnancy or feeding needs: [details or none known]
   - Food and serving information I want estimated: [foods and amounts, if known]
   
   Return the answer in plain British English. Do not use calorie targets unless you can explain that they are only rough estimates and that I should not use them as medical advice.

   Open it prefilled in ChatGPT or Claude, or copy it into Gemini, which takes no prefill link.