Tools & calculators
50 of them, grouped by what you were doing when you needed one. Each solves a problem somebody actually has, shows its working, and states what it assumes. None of them hides the arithmetic, and none of them names a product to buy.
Work out a number
You have the figures and need the one they imply — a ratio, a conversion, a size, a setting. Each shows its working.
Astronomy
“The box says 675× magnification. What will this telescope actually show me, and which eyepiece should I use for what?”
Telescope & eyepiece calculator
Astrophotography
“Will the Andromeda Galaxy fit in my frame with this telescope, and are my camera’s pixels the right size for it?”
Field of view and image scale calculator
Pottery
“I need a finished dish exactly 220mm across to fit a shelf. How big do I make it wet?”
Clay shrinkage calculator
Crochet
“My gauge does not match the pattern. How many stitches do I actually chain to get the width I want?”
Crochet & knitting gauge calculator
Knitting
“The pattern says work 60 rows. My row gauge is not the pattern’s — how many rows do I actually need for 21cm?”
Knitting row and length calculator
Model railways
“How big is a real door in OO — and why does my track gauge not match?”
Scale converter
Cycling
“Is this gear tall enough for the flat, and low enough for that climb?”
Gear ratio calculator
Music production
“My delay pedal is in milliseconds and my project is at 128 BPM. What do I set it to, and what if I want a dotted eighth?”
Tempo, delay and modulation timing
Home brewing
“What strength is this, and has it actually finished fermenting?”
ABV estimator
Running
“What pace do I need to hold, and what should the clock say at halfway?”
Running pace calculator
Indoor rowing
“I did 2,000m in 7:30. What split was that — and if I want to hold 1:55, what would a 5k take?”
Rowing split converter
Automotive detailing
“The label says 1:10 and my bottle is 500ml. Is that 50ml of product, or something else?”
Dilution calculator
Home espresso
“I pulled 18 grams into 41 grams in 33 seconds. What ratio was that, and what should I have been aiming at?”
Espresso dose and ratio calculator
Sourdough
“The formula says 75% hydration and 20% starter. How much water actually goes in the bowl, and does the starter count?”
Baker’s percentage calculator
Pattern drafting
“What measurement should the pattern piece actually be?”
Pattern ease calculator
Knifemaking
“The stock is 3.5mm and I have ground a 15mm bevel. What angle is that, and how does it compare with the one I ground last time?”
Bevel angle calculator
Luthiery
“I am building to a 648mm scale. Where does every fret slot go, measured from the nut?”
Fret position calculator
Fishkeeping
“How much water is actually in this tank, and how much is a 25% change?”
Aquarium volume and water change
Sauna building
“What size heater does this room need, and does the glass door change the answer?”
Sauna volume and heater sizing
CNC routing
“How fine a stepover do I actually need, and what is it costing me in run time?”
Surface finish and stepover
Robotics
“How long will this pack run my robot, and is it the reason the board keeps resetting?”
Robot battery runtime calculator
Home automation
“The box said two years and it died in four months. Where is the charge actually going?”
Sensor battery life calculator
Game development
“I am targeting 60 fps. How much time is that per frame, and does what I just profiled actually fit inside it?”
Frame budget calculator
Hydroponics
“The bottle says 2ml per litre. My tank is 24 litres and I am only changing half of it. How much of each part goes in?”
Nutrient solution calculator
Archery
“I am halfway through a round on 287. Is that any good, where will I finish, and what do I need to shoot to beat my personal best?”
Archery score and round projection
Home machining
“What drill do I use before tapping M6, and what size hole does an M6 bolt pass through?”
Metric thread and tapping drill reference
Work out how much to buy
The question asked in a shop, or in front of a website with a minimum order. Buying twice costs more than buying once.
3D printing
“The slicer says 34 cm³. Is there enough left on this spool to finish it, and what is this print actually costing me?”
Filament, weight and cost estimator
Crochet
“How many balls do I need for a blanket this size, in this yarn?”
Yarn quantity estimator
Dressmaking
“The envelope says 2.2 metres — is that enough for this fabric?”
Fabric quantity estimator
Natural dyeing
“The recipe says 15% alum and 50% madder. Fifteen per cent of what, and how much do I actually weigh out for this skein?”
Dye bath calculator
Upholstery
“How much fabric do I need for this chair, and how much more does the pattern repeat cost me?”
Upholstery fabric estimator
CNC routing
“How many of these come out of one sheet, and how many sheets do I order?”
Sheet yield calculator
Corsetry
“How much coutil, how many bones and what length busk do I actually need — including the mock-ups nobody warns you about?”
Corset materials estimator
Shed building
“How many boards do I actually order to clad this, and why did the last lot come up short?”
Cladding quantity estimator
Smallholding
“What does it actually cost to fence this paddock, and why is the merchant’s number so much bigger than mine?”
Stock fencing quantity and cost
Mould making
“How much silicone do I actually mix for this block mould — and how much do I order, given it is sold by weight?”
Silicone volume estimator
Plan a session, a trip or a project
Time, weight, money and pace, worked out before you commit to them rather than discovered part-way through.
Birdwatching
“What is this actually going to cost me in the first year, including the things nobody mentions?”
Hobby startup cost estimator
Game mastering
“I have prepared six scenes and three hours. How long does each actually get, and is that enough for anything to happen?”
Session time budget
Marathon running
“I want to run four hours. What pace is that, what should the clock say at 10k and halfway, and how much does starting slightly slower actually cost me?”
Race pace and split planner
Running
“I am doing three minutes running, two walking, for half an hour. How far is that actually, and how many cycles?”
Run/walk session planner
Triathlon
“What will I actually finish in, and how much of that is transitions?”
Triathlon race plan
Hiking
“How long will this route take me — not an average walker, me?”
Hiking time estimator
Bikepacking
“Does the day I have planned actually fit in the daylight I have?”
Bikepacking day planner
Fastpacking
“What is my base weight, and which three things are actually making it heavy?”
Base weight calculator
Campervan conversion
“The plate says 3,500kg. How much of that have I already used, and is there anything left for water and luggage?”
Van payload calculator
Fiction writing
“I want to finish a draft. At the rate I actually write, and with the weeks I am actually going to lose, how long is that?”
Drafting target planner
Charcuterie & curing
“How far through drying is this piece, against the target my recipe gave me?”
Curing weight-loss tracker
Choose between things you could buy
Specifications turned into the difference you would actually notice. None of them names a product to buy.
Disc golf
“I throw about 60 metres. Which flight numbers should I be looking for, and what will this disc actually do?”
Disc golf flight helper
Birdwatching
“These two pairs are the same price. Which is better for what I do?”
Binocular specification comparison
Padel
“Round, teardrop or diamond — and what weight?”
Padel racket selector
Tools we know are missing
Listed openly rather than kept to ourselves. If one of these is the thing you came here for, that is worth us knowing.
What can I see tonight?
PlannedWould combine Bortle class, aperture and lunar phase into a realistic target list rather than a catalogue of things you cannot see.
The problem: “Given my sky, my equipment and tonight’s moon, what is actually worth looking at?”
Why it is not here yet: It needs a catalogue of objects with surface-brightness figures behind it, and we do not have one yet. It is the question every beginner actually asks, which is why it is here rather than forgotten.
For Astronomy
Arrow spine and draw weight reference
Worked out in detailWould convert between marked limb weight and actual draw weight at your draw length, and indicate an appropriate spine range.
The problem: “What spine arrow do I need for my draw weight, draw length and point weight?”
Why it is not here yet: Held back deliberately. The draw-weight conversion is safe to publish; the spine half is not, because spine selection depends on manufacturer-specific charts and getting it wrong produces arrows that fly badly and, at the extremes, unsafely. It needs figures from the manufacturers, with their permission, before we could publish it.
For Archery
Firing schedule helper
PlannedWould translate a target cone and clay body into a ramp-and-hold schedule with the reasoning for each segment.
The problem: “What ramp rate and hold should I use for this clay and this glaze?”
Why it is not here yet: Requires manufacturer and standards sourcing before it can be published — a wrong firing schedule wastes a kiln load and, with the wrong glaze, produces ware that is not food safe.
For Pottery
Will this hobby fit my week?
Worked out in detailWould filter the catalogue by available time, session length and travel requirement, and show what genuinely fits rather than what sounds appealing.
The problem: “I have three hours a week and no free weekends. What can I realistically take up?”
Why it is not here yet: It overlaps the hobby finder so heavily that it probably belongs inside it rather than beside it. Listed here so the question stays open rather than being quietly dropped.
For Journaling
Which orienteering course should I enter?
PlannedWould map navigation experience and running pace to a colour-coded course and an expected finishing time.
The problem: “Which colour course is right for me, and how long will it take?”
Why it is not here yet: The colour table on the activity page already answers most of it, so this would add less than it looks.
For Orienteering