Why the number surprises people
Take a plain bent: two eight-by-eight posts fourteen feet long, one eight-by-twelve tie beam twenty-four feet long, four four-by-four braces four and a half feet long. That is seven sticks. Most people, asked to guess, land somewhere under a thousand pounds. The posts alone are 149.3 board feet, the tie beam is 192, the braces add 24, and at forty pounds per cubic foot the assembled bent comes to 1,218 pounds. It is not the piece count that does it — it is that a solid eight-by-eight has more than five times the section of a 2x8, and heavy timber is frequently handled green, which is to say full of water.
Density is doing more of the work in that figure than anything else. The same bent at 30 pounds per cubic foot weighs 913; at 55 it is 1,674. Nothing about the frame moved. That is why the density field is first on the form and why it has no default that pretends to be authoritative — it should come from a species reference for the timber as it will be on the day, or from putting a piece on a scale.
What a centre of gravity is and is not
A bent is assembled lying flat on the deck and stood up about its feet, so the useful way to describe where its weight sits is as a distance along the bent from the sill end. The arithmetic is the weighted mean: each group weight multiplied by its distance, all of that summed, divided by the total weight. Groups near the top pull the result upward in proportion to their weight, which is why the tie beam dominates on a typical bent — it is both the heaviest single member and the furthest out.
| Group | Weight | Distance | Moment |
|---|---|---|---|
| 2 posts, 8x8x14 | 498 lb | 7 ft | 3,484 ft-lb |
| 1 tie, 8x12x24 | 640 lb | 13.5 ft | 8,640 ft-lb |
| 4 braces, 4x4x4.5 | 80 lb | 11 ft | 880 ft-lb |
| Total | 1,218 lb | 10.68 ft | 13,004 ft-lb |
What it is not is a rigging answer. It is one number in one direction, calculated from an assumption that every member sits on the centreline of the bent, which real bents routinely violate — one brace instead of two, a post off centre, a member framed to one face. It also says nothing about how a load behaves once it is off the ground, which is where the questions that matter actually start.
The line this page does not cross
It will report a weight and it will report a balance point. It will restate a rating you enter, word for word, next to the weight, and it will not compare them. That refusal is deliberate rather than coy: a rating is not a single number a weight can be measured against. It depends on the configuration, the angles, the geometry, the condition of the equipment, how the load is attached, what else is in the system, and who is responsible for the whole of it. A page that put a tick or a cross next to those two numbers would be inventing the six facts it does not have.
Raising a bent is rigging. A bent that goes over during a raising does so quickly and heavily, and people have died underneath. Weight and balance are two of many inputs to a plan made by people who are trained, equipped and accountable. Use these numbers as inputs to that conversation, not as a substitute for it.
Getting the distances right
The one input people get wrong is the distance, not the size. It is measured along the bent from the sill end to the centre of mass of that group, which for a plain post is half its length and for a tie beam at the head of a fourteen foot post is a little under fourteen feet — the tie sits above the posts, so its centre is roughly the post length plus half the tie depth. Braces cluster near the top on a knee braced bent and near the middle on others. If a group is spread out, put it where its own centre of mass is, not where the nearest joint is.
Questions people ask
What density should I use?
The one that matches your timber on the day you handle it, from a species reference or a scale. It is the single largest source of error in the result, because weight is directly proportional to it. Green timber can be half again as heavy as the same species air dried, and frames are frequently cut and raised green. This page has no way to know which you have.
Does the calculator tell me whether my equipment can lift the bent?
No, and it will not, even if you enter a rating. A rating is not a number a weight is simply compared against — it depends on configuration, angle, geometry, condition, attachment and the rest of the system. If you enter a figure it is printed back exactly as entered, beside the calculated weight, with no comparison drawn. Deciding whether a lift can be made is the job of people with rated equipment, training and responsibility for it.
Why is the centre of gravity measured from the sill?
Because a bent is assembled flat and raised about its feet, so distance along the bent from the foot is the direction that describes it. It is a one-dimensional figure: the weighted mean of your group distances. It assumes everything sits on the centreline, which asymmetric bents do not, and this page does not calculate the across-the-bent balance point at all.
Should the weight include the pegs and the ironwork?
If you want the assembled figure, yes — that is what the extra weight field is for. It is added to the total and assumed to sit at the timber centre of gravity, so it changes the weight without moving the balance point. If the ironwork is concentrated somewhere specific and heavy, it is more honest to enter it as an Other member group with its own distance.
Does it account for the mortises cut out of the timbers?
No. The volume is nominal timber volume, which is slightly more wood than a joined bent contains. The overstatement is small — a few mortises out of a piece holding thousands of cubic inches — and it errs on the heavy side, which is the direction you want an error in a weight to go. It is nowhere near large enough to offset getting the density wrong.