Why Two Converters Give You Different Answers

It is a genuinely annoying experience. You look up how many grams are in a cup of flour, get 120 on one site, 125 on another and 140 on a third, and have no way to tell which one to believe.

There are four separate causes, and once you can tell them apart the disagreement stops being mysterious.

1. They assume different measuring techniques

This accounts for most of it. Flour spooned into a cup is about 120 grams; flour scooped straight from the bag is about 140. Both figures are honest measurements — they are just measuring different actions.

The problem is that hardly anyone says which they used. You get a number stripped of the context that would let you reconcile it with anything else. A site publishing 140 is not wrong; it is describing a technique the site publishing 120 rejected.

2. Rounding conventions

Some sources round to memorable figures. Granulated sugar is very commonly published as 200 grams per cup because it is a clean number, while careful measurement puts it closer to 198. Butter is published as 227 grams, which is the exact conversion of 8 ounces, but you will also see 225 from sources rounding to the nearest 25.

These differences are trivial in practice — a 2 gram error on sugar will never be detectable in a finished bake — but they explain small inconsistencies that can make you doubt an otherwise reliable source.

3. Genuine product variation

Some ingredients really do differ, and no amount of careful measurement will make sources agree:

• Kosher salt is the worst case. Crystal size varies so much between brands that a cup can range from roughly 145 grams to over 240. A single figure for "kosher salt" is close to meaningless without naming the brand. This is why serious recipes specify the brand for salt and nothing else.
• Shredded cheese and grated vegetables depend entirely on the coarseness of the shred. A fine grater and a coarse one give different weights from the same cheese.
• Brown sugar depends on packing pressure, which is why recipes say "packed" — and why an unpacked cup can be a third lighter.
• Chopped nuts vary with how finely they are chopped. Whole almonds are about 143 grams a cup; sliced almonds only 92, because the slices stack with more air between them.

4. Copying without checking

This is the least discussed and probably the most common. Conversion figures propagate between websites without anyone re-measuring. A rounded value published once gets copied, then copied again, and eventually appears on dozens of sites — which makes it look independently corroborated when it has a single unverified origin.

You can occasionally catch this in the wild. We have seen a published dataset ship a brown sugar figure of 220 grams per cup while its own source code carried a developer note saying the cited authority actually lists 213, with a comment to update it later. The wrong number was public; the correction was not.

How to judge a source

A density figure is more trustworthy when it tells you three things:

1. Which technique it assumes — sifted, spooned, scooped, packed.
2. Where the number came from — a named authority, not "the internet".
3. When it was last checked.

Most sites publish none of these. It is worth preferring the ones that do, even when their numbers are less convenient. We publish all three for every value in our open density dataset, including an honest label on the figures we have not yet corroborated against a primary source.

How much precision you actually need

Before you spend more time on this, it is worth knowing where accuracy matters:

For the top two rows, pick any reasonable figure and move on. For the bottom three, the disagreement between sources is worth caring about — and a scale settles it permanently.

Reconciling two sources by hand

Suppose one site says 120 g per cup of flour and another says 140. Rather than picking the one you like, work out which action each describes. The ratio is 140 ÷ 120 = 1.17 — a 17% difference, which matches almost exactly the known gap between spooned and scooped flour.

That tells you the sources are not in conflict at all: they are describing the two ends of the same technique range. Once you know which technique you use, you know which number applies to you.

When two figures differ by only 1–2%, it is rounding and you can ignore it. When they differ by more than 20% and the ingredient is not compressible, one of them is probably wrong.

When you genuinely cannot tell

Sometimes there is no way to resolve it from the outside. A few fallbacks, in order of preference:

1. Use the recipe's own figures. If it gives grams as well as cups, those were what the author tested. Nothing beats that.
2. Prefer the source that shows its working. A stated technique and a named source is worth more than a rounder number.
3. Take the middle for forgiving recipes. For cookies or muffins, splitting the difference costs you nothing.
4. Weigh it and settle the question permanently.

What we do about it

We store separate densities per technique rather than averaging them into one misleading number, we record the source and date for every value, and we say plainly on the page when a figure is still provisional. That will not make us agree with every other converter. It should at least make it clear why we differ.