What this calculator does
Horses are fed forage as a percentage of bodyweight, and two per cent is the usual starting point. A 500 kg horse therefore needs 10 kg of dry matter a day, and because hay is around 90 per cent dry matter, that is 11.1 kg of hay as fed. Over thirty days it is 333 kg, which is about 17 small bales.
The step people skip is the dry matter conversion. Weighing out 10 kg of hay to meet a 10 kg dry matter requirement under-feeds by roughly ten per cent, every day, which is the kind of slow shortfall that shows up as condition loss rather than as an obvious problem. The other half of the same mistake is counting flakes instead of weighing: flake weight varies enough between bales that it is not a unit of measurement at all.
The formula
Dry matter needed is bodyweight × feeding rate. Whatever share comes from pasture is taken off, and the rest is converted from dry matter to hay as fed by dividing by the dry matter percentage: hay dry matter ÷ dry matter %. Bales and cost follow from the bale weight and price you enter, so small squares, large squares and rounds all work as long as you weigh one.
| Term | Meaning |
|---|---|
| Dry matter | What is left after the water. The basis every forage requirement is stated in. |
| As fed | The weight you actually put over the fence, water included. |
| Feeding rate | Forage as a percentage of bodyweight. Usually 1.5 to 2.5 per cent. |
| Pasture share | The part of the daily intake grazing already provides. |
The inputs explained
| Field | What to enter |
|---|---|
| Horses | How many horses you are feeding at this weight and rate. |
| Bodyweight each (kg) | Bodyweight in kilograms. A weight tape or the heart-girth estimate beats an eye estimate. |
| Feeding rate (% of bodyweight) | Forage as a percentage of bodyweight. Two per cent is the common maintenance figure. |
| Share of intake from pasture (%) | Share of daily intake coming from pasture. Set it to zero for a horse off grass entirely. |
| Dry matter of the hay (%) | Dry matter of the hay. Around 90 per cent for cured hay, much lower for haylage. |
| Bale weight (kg) | Weight of one bale. Weigh a few and average them rather than using the nominal figure. |
| Bale price ($) | Delivered price of one bale. |
| Days to plan for | Days you are planning for, whether that is a week, a month or a winter. |
When to use it
Buying hay for a season
Set the days to the length of the feeding period and read the bales figure. Add a margin for waste and a late spring rather than ordering exactly.
Feeding a horse off grass
Leave the pasture share at zero. A horse with no grazing takes its whole forage requirement from hay, which is where the daily figure jumps.
Switching to haylage
Change the dry matter figure rather than the feeding rate. Haylage can be 60 per cent dry matter or less, so the as-fed weight rises sharply for the same nutrition.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How much hay does a horse need by weight?
Only the bodyweight of the horse changes.
| Bodyweight | Hay a day per horse | Hay for the period | Cost for the period |
|---|---|---|---|
| 300 kg | 6.7 kg as fed | 200 kg | $120.00 |
| 400 kg | 8.9 kg as fed | 267 kg | $160.00 |
| 500 kg | 11.1 kg as fed | 333 kg | $200.00 |
| 600 kg | 13.3 kg as fed | 400 kg | $240.00 |
| 700 kg | 15.6 kg as fed | 467 kg | $280.00 |
What does the feeding rate change?
The horse is fixed and only the percentage of bodyweight changes.
| Feeding rate | Hay a day per horse | Dry matter a day | Cost for the period |
|---|---|---|---|
| 1.5% of bodyweight | 8.3 kg as fed | 7.5 kg | $150.00 |
| 1.75% of bodyweight | 9.7 kg as fed | 8.8 kg | $175.00 |
| 2% of bodyweight | 11.1 kg as fed | 10.0 kg | $200.00 |
| 2.25% of bodyweight | 12.5 kg as fed | 11.3 kg | $225.00 |
| 2.5% of bodyweight | 13.9 kg as fed | 12.5 kg | $250.00 |
Questions
Why convert for dry matter at all?
Because the requirement is stated in dry matter and hay is not dry. At 90 per cent, feeding 10 kg of hay delivers 9 kg of dry matter, so you are 10 per cent short before anything else goes wrong. For haylage at 60 per cent the gap is far larger.
Can I just count flakes?
Not reliably. Flakes vary with how the baler was set and how the bale has settled, and the same number of flakes can differ by several kilograms between bales. Weigh a few flakes once and you will usually find the ration is not what you thought.
How do I estimate the pasture share?
It is a judgement, and it moves with the season. A rough approach is to set it high in spring on good grazing and to zero in winter or on a bare paddock, then check it against body condition rather than trusting the number.
Does this cover hard feed or supplements?
No, forage only. Concentrates, balancers and supplements are fed to a different logic and should be counted separately, though they do count toward the total dry matter intake.
How much should I add for waste?
That depends entirely on how it is fed. Round bales in a paddock without a feeder can waste a quarter or more, while small bales in a net waste very little. Weigh what goes out and what gets cleaned up for a week to find your own figure.
For the bodyweight that drives all of this, see horse weight estimate. Round pen panel count covers the yard, and livestock stocking rate handles how much grazing the land itself will carry.