While I was an editor at a woodworking magazine, I received a lot of questions about the projects we published. Here are two questions that were tricky to answer:
- How much does that project weigh?
- How much does that project cost to build?
These aren’t really questions that I ask myself as a builder unless I’m making something for NASA or a customer on a crazy tight budget. But readers deserve an answer better than, “I dunno.”
So here’s how to spitball both.
Weight
There are lots of published statistics of the average weight of each species. Usually this is listed as the “weight per cubic foot” of that wood. Let’s take koa as an example. A cubic foot of koa is 38 lbs. If you divide that by 12, then you know the weight of one board foot of koa – 3.16 lbs.
Note that this an average weight at an average moisture content.
Here’s a list of species and their weights that I like to use.
Now you need to know how much board footage of wood is in the project. Luckily, there are lots of nice web-based board-footage calculators out there. You simply punch in the dimensions of each part and they spit out how much board footage is in there.
For example, a tabletop that is 3/4” x 26” x 96” is 17.33 board feet.
Here’s a simple board footage calculator that I use.
So if I build that tabletop out of koa, it will weigh 17.33 x 3.16 or 54.88 lbs.
Cost
This is tricky, because every lumberyard is different. I can buy ash for $1/board foot. Perhaps you cannot. So I use WoodFinder to look up average prices. Type in the species and it will call up places that carry that species. One of the places I looked at tonight had koa at $36/board foot.
So I can use the board footage calculator to determine that 17.33 board feet of koa will cost me $623.88.
Hmmm. Maybe koa isn’t right for me.
— Christopher Schwarz
awsome calculator
Maybe not, but it would be a great table.
…said the man with the koa monkey on his koa back.
How much does weight really matter in any furniture you don’t pick up regularly? I mean, I care what a chair weighs, but an armoire or dining table, etc., not so much.
Cost? I guess the questions are about materials alone? Plenty of other cost elements like the tools and overhead overhead of maintaining a shop and your time and so forth. Mostly you don’t build your own furniture to save money ;). And if you’re going to take the time to build it as a hobbiest, the cost of materials – within reason – is a silly place to scrimp. If you make 25 excellent pieces you and your descendents will enjoy over a lifetime it’s a lot. And who’s gonna remember an extra $300 for nice wood on a piece?
I’ve used wolfram alpha to calculate the weight of a built workbench before
((8*(5cm*7cm*35cm) + 4*(70cm*11cm*11cm) ) * density of pine) + ((160cm*11cm*60cm) * density of beech) in kilograms
http://www.wolframalpha.com/input/?i=%28%288*%285cm*7cm*35cm%29+%2B+4*%2870cm*11cm*11cm%29+%29+*+density+of+pine%29+%2B+%28%28160cm*11cm*60cm%29+*+density+of+beech%29+in+kilograms
These are my two most common questions too! I don’t think people actually want or need this information but it’s something concrete they can ask and take away from the conversation. Not, ‘how freaking complicated was it to get all that worked out in your head and on paper and get the materials together and actually put it together in a competent way?’
Reblogged this on Paleotool's Weblog and commented:
Two questions I seem to get every day. Not that I think most peole need or really want these numbers but it give a concrete question and (possibly) a simple number to take away.
How much does that weigh?
How much will that cost me to build?
Click to READ ON.
Chris,
How much do you add to factor in time? Do you or does the industry have a set rate for time set any project? Is time spent designing, sharpening, buying timber all part of the job? In the Time Store time is money.
Cheerio,
Virgil.
PS Finished my Roubo bench about six weeks ago. One of the most gratifying things I’ve ever done. Thanks for the inspiration.
Virgil,
I have an hourly shop rate – just like an auto mechanic – that gets added onto materials for every commission. That rate includes overhead (electricity, sharpening, maintenance, taxes etc.) and profit.
That’s why I always camp at state parks or national parks… KOA’s too expensive!
a project is also going to take a lot longer depending on how you organize it. if you have a few solid days, awesome! but it you have two hours here and there after your day job, it’s gonna take a while.