Short answer
Describe the plate in parts rather than as one dish, add a deliberate allowance for cooking fat you did not see going in, and record the whole thing as an estimate. Then stop thinking about it.
The goal is a number that is roughly right and honestly labelled, not one that is precise. A meal like this is going to carry more uncertainty than anything you cook yourself, and pretending otherwise is worse than accepting it.
Why this is harder than eating out
Restaurants are more tractable than people expect. Chains publish nutrition data, menus name the components, and portions are standardised because consistency is the business. Tracking macros when eating out covers that workflow, and most of it depends on information a home kitchen does not produce.
A meal cooked by a friend or a family member has no menu, no published figures, no standard serving, and a recipe that exists only in someone's head and changes every time they make it. You also usually cannot see the cooking, so the parts of the meal that carry the most energy went in while you were in another room.
The fat you did not see going in
This is the single largest source of error, and it is invisible by the time the plate reaches you. Oil in the pan, butter finishing a sauce, a knob added to vegetables, oil in a marinade, cream in a mash. None of it is visible in the finished dish and all of it counts.
Home cooking is often more generous with fat than restaurant portions people are wary of, because there is no portion control and no reason to be careful. A tablespoon of oil is about 120 Calories, and a dish that used three across a pan you never saw is carrying a few hundred Calories nobody can point at.
The practical move is to assume there was more fat than the dish looks like it contains, and to add an allowance rather than leaving it at zero. The cooking oil calorie calculator gives you a sense of what plausible amounts are worth, and if the dish had a sauce or dressing on it the sauce and dressing calculator covers that separately.
Break the plate into parts
Logging "Mum's lasagne" asks for a number nobody has. Logging the components asks a series of much easier questions.
Look at the plate and name what is on it in rough amounts: a piece of chicken about the size of your palm, roughly a cup of rice, a spoonful of sauce, some salad with dressing on it. Each of those you can estimate reasonably. The dish as a whole you cannot.
This is also the description you want to write down rather than just the total, because a note you can read next week is correctable and a bare number is not. The meal description builder is built for exactly this, and writing better meal descriptions covers the details worth including.
If you do happen to know the recipe, that changes the problem entirely and the recipe macro calculator will divide a known batch by servings or by cooked weight.
What each part of the plate is worth
You cannot weigh anything at someone else's table, so the useful skill is converting what you can see into a number. These are the reference points worth memorising, because they cover most of what turns up on a plate.
| What you can see | Roughly | Calories |
|---|---|---|
| Palm, fingers excluded | about 100 g cooked chicken or fish | 165 Cal |
| One cupped hand | about 90 g cooked rice | 117 Cal |
| One cupped hand | about 90 g cooked pasta | 142 Cal |
| A matchbox | about 30 g cheddar | 121 Cal |
| Two thumbs, end to end | about 1 tbsp of oil in the pan | 119 Cal |
| One thumb tip | about 1 tbsp of butter | 102 Cal |
Look at the last three rows next to the second. A cupped hand of rice is about 117 Calories and two thumbs of cooking oil is about 119. They cost the same, and only one of them ever gets logged. That is the whole problem with a meal you did not cook, in one comparison: the carbohydrate is visible and gets counted, and the fat that went in during cooking is invisible and does not.
Hands vary, so these are starting points rather than measurements. If you want to calibrate yours, weigh a portion of rice at home once against your own cupped hand and adjust the figure you carry around. Doing that a single time is worth more than trying to be precise at a dinner table.
Calorie figures are USDA reference values for the stated weights: 165 Cal per 100 g cooked chicken breast, 130 per 100 g cooked white rice, 158 per 100 g cooked pasta, 402 per 100 g cheddar, 119 per tablespoon of oil and 102 per tablespoon of butter. The hand comparisons are common portion-estimation guidance and vary with hand size; the weights they map to are the approximate part, not the calories.
You were served, you did not portion
Worth naming because it changes what you are estimating. A portion someone else plated is whatever they thought was a reasonable amount for you, which is frequently larger than what you would have taken, and there is often a second helping involved.
So estimate the amount actually on your plate rather than a standard serving of the dish. If you had seconds, log both. Comparing what you were given against a serving size from a database entry is comparing two unrelated things.
For picturing a weight without a scale, how many calories are in 100 grams shows what that amount looks like across common foods, and tracking without a food scale covers hand references and household measures.
Afterwards, leave it alone
Record it, mark it as an estimate, and resist revisiting it. There is no additional information coming, so a second guess is not a better guess, and re-editing a meal you cannot verify is a way of worrying rather than a way of improving the log.
One meal like this a week barely moves a weekly average. If it becomes most of your meals, the answer is not better estimating but a different approach, and how accurate calorie tracking needs to be covers where precision genuinely pays. The weekly calorie average calculator puts a single uncertain day in the context of a complete week, which is usually reassuring.
What this cannot do
It will not give you an accurate number, and no method will for a meal you did not cook and cannot weigh. What it gives you is an honest estimate that keeps the log continuous, which is worth more than a gap or an abandoned week.
This is general information for adults. If tracking is producing guilt, anxiety around shared meals, or avoidance of eating with other people, that is a reason to step back and speak with a clinician or registered dietitian rather than to estimate harder.
Do not get the scale out at someone's table
Weighing food at a dinner someone cooked for you changes the meal for everyone at it, and the accuracy you gain is not worth what it costs. The same applies to photographing every dish, interrogating the cook about ingredients, or visibly logging during the meal.
Look at the plate, remember what was on it, and write it down afterwards. A rough estimate recorded calmly is a better outcome than a precise one that made a family dinner awkward.
If tracking is making shared meals stressful rather than just imprecise, that is worth paying attention to. Some people find it easier to log these occasions as a rough estimate and move on, and some find it easier not to log them at all. Both are reasonable.