How this instrument works
Dry matter (DM) is what remains of a feed sample once every trace of water has been removed — everything else, protein, fiber, sugars, minerals, is dry matter, and it's what livestock actually derive nutrition from. Two forages can look and weigh identically 'as-fed' yet supply very different amounts of real nutrition if their water content differs, which is why feed rations, purchase prices and storage decisions are built on dry matter, not raw wet weight.
The calculation itself is a direct ratio: divide the dry weight (what's left after full oven-drying to a constant weight) by the wet, as-fed weight, then multiply by 100 to express it as a percentage. There's no estimation or curve-fitting involved — this is a definitional measurement, so its accuracy depends entirely on how completely and accurately the sample was dried and weighed, not on any formula assumption.
Typical dry matter ranges vary widely by feed type: fresh-cut silage commonly runs 30-40% DM, baled hay 85-90% DM, and pasture forage can be as low as 15-25% DM depending on growth stage and recent rainfall. Knowing a batch's actual DM% lets a producer convert a scale weight of 'as-fed' feed into the pounds of true nutrition being delivered, and to correctly compare the cost or value of forages with very different moisture levels.
- Weigh your forage or feed sample as collected (undried) and enter that figure into Wet (as-fed) weight.
- Dry the same sample fully — oven-dry to a constant weight, or use a microwave or forage moisture tester following standard method — then enter the result into Dry weight (after full drying).
- Read Dry matter (%) directly beneath the inputs; it recalculates instantly as either weight changes.
- Use the same units (grams, ounces, pounds) for both weights — the ratio is unitless, so as long as both entries match, the percentage comes out correctly regardless of which unit you choose.
- If dry weight is entered greater than wet weight, the instrument will flag it — a sample cannot weigh more after losing water than it did before drying.
Worked example — 100 g wet, 35 g after drying
A 100 g sample of freshly cut silage is oven-dried to a constant weight of 35 g. Enter 100 into Wet (as-fed) weight and 35 into Dry weight (after full drying); Dry matter (%) reads 35.0: (35/100) x 100 = 35.0%.
That 35% DM reading sits right in the realistic 30-40% range typical of fresh-cut silage, meaning 65% of the original sample's weight was water that evaporated during drying — a useful check that the drying process behaved as expected and the sample wasn't unusually wet or unusually dry for the crop and cutting stage.
Questions
Why does dry matter matter more than as-fed weight for feeding livestock?
Because water carries no nutrition — a ton of 30%-DM silage delivers only 600 lb of actual dry matter, while a ton of 90%-DM hay delivers 1,800 lb, three times the nutrition for the same as-fed weight. Rations, intake targets and feed comparisons are built on dry matter precisely because it strips out the water and leaves only what the animal can actually use.
What's a typical dry matter percentage for hay versus silage?
Baled hay is typically 85-90% DM because it's field-cured and dried before baling, while silage is fermented and stored wet, typically 30-40% DM for direct-cut material and somewhat higher for wilted silage. Pasture forage varies even more, often 15-25% DM depending on growth stage, species and recent rainfall, which is why grazing intake calculations lean heavily on an accurate DM reading rather than a rule of thumb.
How do I actually dry a forage sample to measure dry weight?
The reference method is oven-drying a weighed sample at a controlled temperature until its weight stops changing between successive weighings — a 'constant weight' that confirms all free moisture is gone. Field alternatives include microwave drying in short bursts with cooling and reweighing between each, or an electronic forage moisture tester, both faster but slightly less precise than a lab oven.
Can I use pounds for one weight and grams for the other?
No — both weights need to be in the same unit, since the formula is a straight ratio and mixed units would give a meaningless result. It doesn't matter which unit you pick (grams, ounces, pounds, kilograms) as long as wet weight and dry weight are both measured and entered in that same unit.
What does it mean if my dry weight comes out higher than my wet weight?
It means something went wrong in weighing or recording, not that the sample gained matter — a sample can only lose weight as water evaporates during drying, never gain it. Check that the scale was tared correctly, that you're using the same sample both times, and that the wet weight wasn't recorded after some moisture had already evaporated.