Everyday Calculators

Built for the practical questions that do not belong to money, health or the house. Three of them recur: ordering across borders and finding the size on the box is not the size that fits, pricing a project before buying the materials, and turning a scorecard or a watch into a number. Sports and DIY & Materials were categories of their own until 2026-09-23, with two and three calculators between them; a category that small reads as abandoned, so those tools moved here and their old addresses redirect.

Start from the measurement, not the size. The Shoe Size Converter works from your actual foot length in centimetres and shows both US women’s scales, which disagree by half a size; the Clothing Size Converter works from chest, waist and hip measurements, and marks which national numbers are real measurements and which are only conventions; the Ring Size Converter works from a circumference in millimetres, because no two published ring charts agree; and the Bra Size Converter works from two measurements and gives both band methods plus the sister sizes, since a UK G is not a US G.

In the kitchen, the Cake Pan Size Converter scales a recipe to a different tin by area rather than diameter — the obvious arithmetic is wrong by roughly a factor of two — and the Baker’s Percentage Calculator converts a bread formula between percentages and grams with the levain split out, because the percentages are of the flour alone and total nearly 200.

On the bike, the Bicycle Tire Pressure Calculator turns riding weight, bike weight, front/rear split, tyre width, tyre type and terrain into a front and rear pressure, built from Frank Berto’s openly published tyre-drop research rather than a proprietary model. Treat its result as a starting point to ride and adjust, always inside your tyre and rim manufacturer’s printed range.

Use the Concrete Calculator for a rectangular slab or footing, or a circular slab or column — enter the dimensions and a waste factor to get cubic yards (how ready-mix is ordered) and 40, 60, and 80 lb bag counts (how small DIY pours are bought) side by side.

Use the Paint Calculator for a room repaint — enter its dimensions, doors, windows, and coats to get gallons needed, with an adjustable coverage rate for textured or porous surfaces.

Use the Gravel Calculator for a driveway, path, garden bed, or French drain — enter the area and depth to get cubic yards/metres and tons/tonnes for crushed stone, pea gravel, or road base, in US or metric units.

Two tools. The first covers both bat-and-ball sports, because they need different arithmetic rather than different labels. Open the Batting Average Calculator and pick the mode that matches your sport: baseball and softball divide hits by at-bats, cricket divides runs by dismissals. The same page also computes on-base percentage, slugging and OPS beside a baseball average, strike rate and bowling average beside a cricket one, a pooled team or career figure from a list of players or seasons — which is not the same as averaging a column of individual averages — and a pitcher’s opponent batting average.

The second is for runners rather than scorers. The Pace Converter moves between min/km, min/mile and km/h and puts race times beside them, which is the conversion you need when the treadmill reads km/h, the watch reads min/km and the training plan is written in min/mile. It also shows why two paces average correctly over equal distances and not over equal times.

All of it is arithmetic on the counts you enter, so the results are exact — the judgement lies entirely in whether the counts are right, which is a scoring question rather than a mathematical one.

1. 1Measure your foot in centimetres and convert that, rather than converting the size you think you are.
2. 2Take chest, waist and hip measurements and read the US, UK and EU clothing sizes each one implies.
3. 3Measure a ring you already wear around its inside circumference in millimetres before ordering another.
4. 4Scale a recipe by the tin’s area, not its diameter, and compare that against the answer most people reach.
5. 5Choose a rectangular or circular shape and enter the dimensions for the Concrete Calculator, the room dimensions for the Paint Calculator, or the area and depth for the Gravel Calculator.
6. 6Adjust the waste factor (concrete or gravel), coverage rate (paint), or material density (gravel) for your specific job, then read off the order-ready quantity.
7. 7Check each calculator's formula section to see exactly how the quantity was reached, not just the final number.
8. 8Read the limitations before ordering — concrete for anything structural or permitted, paint for primer and trim, gravel for a two-layer driveway base, none of which are included.
9. 9Start in the calculator and pick your sport — baseball and softball share one formula, cricket uses another.
10. 10Read the two formulas side by side to see why a cricket average has no ceiling and a baseball one cannot pass 1.000.
11. 11Settle the walks question: add your walks and hit-by-pitches to see the on-base percentage the batting average refuses to credit.
12. 12Switch sports entirely and convert a running pace between min/km, min/mile and km/h, with the race times that pace implies.

• Converting a size instead of a measurement. Every chart in this section starts from a body measurement for a reason: national size labels are not a single scale with offsets, so converting UK 8 to EU 38 to US 6 through three charts compounds three different approximations.
• Assuming the letters continue to agree. Bra cup letters diverge above DD, so a UK G and a US G are different cups — and shoe charts disagree between the two US women’s scales by half a size before any country changes.
• Scaling a cake recipe by tin diameter. Area goes with the square of the radius, so an 8-inch round to a 10-inch round is a factor of 1.56, not 1.25 — a mistake that shows up as a flat, over-baked cake rather than as an arithmetic error.
• Copying the maximum pressure printed on a tyre’s sidewall. That figure is the tyre’s safe ceiling, not the pressure suited to your weight, and the rear wheel usually needs a few psi more than the front to reach the same tyre drop.
• Keeping a narrow-tyre pressure after fitting wider tyres. A wider tyre needs less pressure for the same 15 per cent drop, which is why the calculator asks for the width you actually run.
• Reading the width off the sidewall instead of measuring the mounted tyre. The same labelled tyre can come up wider on a wide rim, and width enters the formula raised to a power, so a millimetre moves the result.
• Concrete: skipping the waste factor — forms are never perfectly level and some mix is always lost to spillage and overfilling, so ordering the bare calculated volume tends to come up short.
• Concrete: treating a circular field as the radius instead of the diameter — the calculator asks for diameter, matching how tube and post sizes are usually specified.
• Paint: forgetting a second coat, or forgetting that primer is a separate estimate at a lower coverage rate than finish paint.
• Paint: trying to pour an L-shaped room or slab into one rectangle — break complex shapes into simple rectangles and add the results.
• Gravel: using one density figure for a two-layer driveway — the compacted base course and the decorative top layer are usually different materials and should be calculated separately.
• Dividing cricket runs by innings instead of by dismissals — it understates every batter who has a not-out, and the gap widens the more often they finish unbeaten.
• Expecting a walk to lift a batting average. It cannot: a walk is not an at-bat, so it moves neither half of the fraction. On-base percentage is the statistic that credits it.
• Averaging a column of individual batting averages to get a team figure. That gives a bench player with nine at-bats the same weight as a regular with six hundred; the correct figure pools the raw hits and at-bats.
• Comparing a cricket average against a baseball one. They share a name and nothing else — one is runs per dismissal, the other a proportion of attempts.

Nothing in this section makes a decision for you. The sizing tools convert a measurement into the size a chart implies, not into a guarantee that a particular maker’s cut will fit. The materials tools estimate quantity only — they do not size a footing for a load, specify a mix, or price the job. The sports tools are exact arithmetic on the counts you enter, so the judgement sits entirely in whether those counts are right, which is a scoring question rather than a mathematical one.

Each group names what it stands on. The sizing tools are built from published national sizing standards and the length or circumference each size denotes. The tyre pressure comes from Frank Berto’s published tyre-drop research rather than a manufacturer’s chart. The materials tools use standard geometry with bag yields cross-verified against two independent manufacturer data sheets and a waste factor following NRMCA guidance. The sports tools apply the published definitions of a cricket and a baseball average, which differ by more than a label.

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Built and maintained by Jay Sudha · Last reviewed 13 September 2026. See a formula issue, unclear assumption, or broken result? Report it through the contact page.