Monsters to Scale: Rules to determine or estimate the weight of monsters?

In researching this question: Moving Otiluke's Resilient Sphere I could not find any sources that list monster weights or any rules for determining or estimating them.

Not only does this inform the question linked about, but I can see it also helping in other situations as well. For example, hunting creatures while playing under the encumbrance rules strictly.

1. Are there any rules in 5e for determining or estimating monster weight?
2. If there are none, are there any rules from previous editions or houserules that can be implemented to fill the gap?
• Commented Dec 20, 2017 at 16:51

As was mentioned in this related question....game designers aren't generally very good at biology. As you can see in my answer to this question, they slapped a mass on a gelatinous cube, and ended up with a creature less dense than cork.

Now, that said, while there are no rules for this laid out in 5E, there are other resources that may be useful to you.

Released as part of the D&D 3.5 SRD, we have a table of creature size and scale that includes weight ranges for creatures of a given Size. This table can also be found at the bottom of this page in the Hypertext SRD, but the first link is a little easier to access.

If you want more specific information on a given creature, many entries in the 3.5E Monster Manuals included a section on typical height and weight. For example....

An Astral Deva is about 7-1/2 feet tall and weighs about 250 lbs.

3.5E MM, page 11.

A Displacer Beast is the size of a Bengal Tiger, about 9 feet long and weighs about 500 lbs

page 67

However, not every entry has this information. For example, it is lacking in the Dragons section.

As a final option, you can do what the first link in this answer recommends, and make use of the Square Cube law to ballpark a weight.

To use this...take a creature that has a similar body plan to your other creature and look at how different they are in height (or length).

$$Multiplier = NewHeight/OldHeight$$

Now, take the mass of the original creature and...

$$NewWeight = OldWeight*(Multiplier)^3$$

Using this, you can put a ballpark on the weight of a creature based on the weight of an RL creature that has a similar build.

Between these three resources, the table, the specific per-creature entries from 3.5E Monster Manuals, and the square-cube law, that should be enough to let you at least ballpark the weight of any creature.

• This is a very good rule of thumb. Since 5e only uses a number of spaces to indicate general size class, a general weight class should be fine for most creatures. (An Iron Golem would be an exception, for example). Commented Dec 20, 2017 at 21:48

The SRD for D&D 3.5e has this under “Movement, Position, and Distance”, but the core rule books for D&D 5e do not.

• Do you mean the "Table: Creature Size and Scale"? It is from 3.5e SRD, isn't it? Commented Dec 20, 2017 at 17:19
• @enkryptor yes, that's 3.5E SRD Commented Dec 20, 2017 at 17:22
• @enkryptor The footprint consumed by the Sizes that were persisted for 5E is comparable. Tiny takes up 2.5', Large takes up 10', Huge takes up 15', Gargantuan takes up 20(+)'. 5E appears to have simply condensed the top and bottom of the size scale. So, the table is still potentially useful for reference...but is not actual 5E Rules. Commented Dec 20, 2017 at 17:40
• It's a useful reference, but answer should probably clarify that this is from the 3.5 SRD (i.e. not the 5e SRD). Commented Dec 20, 2017 at 19:44
• I've edited the answer to say that the link is to the System Reference Document for D&D 3.5e. Commented Dec 20, 2017 at 19:53